I've been spending a bit of time with the 1.3 Powerplay Beta, and I've been taking advantage of the 1% ship hull and equipment costs to play with the latest ships to be added to the menagerie of vessels: the Imperial Courier and the Lakon Diamondback.
[Edit: 16/07/15 - I posted this before Frontier decided to put out two versions of the Diamondback, so I've added in an extra section to highlight the differences between the Diamondback Scout and the Diamondback Explorer.]
Cost: 2,479,400 Cr
Recommended weapon loadout 1 (Courier/Smuggler): x3 Class 2 Gimballed Pulse Lasers
Recommended weapon loadout 2 (RES Hunter): x2 Class 2 Gimballed Beam Lasers, x1 Class 2 Gimballed Cannon
Why you should fly it: On first inspection, the Imperial Courier seems like an odd little ship. It's a cross between a supercharged Eagle and a Viper. It has three medium-sized weapon hardpoints with good fields of fire, making it more combat effective than the Eagle or Viper, but the standout feature of the Courier is its shield strength. With a 3A shield generator and three 0A shield boosters, the Courier's shield strength rivals that of a Python, which is insane. In combat versus similar-sized ships, I've never lost more than a single ring of shields, even if I've been rammed by my target. The Courier is certainly a tough little ship. Allied with its high speed, it ought to be perfect for blockade running with precious or illegal cargoes. You can easily outrun interdicting ships, who'll never get through your shields by the time that your FSD has cooled down. It's also quick enough to avoid scans outside of stations to prevent you from getting fined on those missions where you have to recover contraband cargoes. The only problem is that the Courier has short legs, especially if it's laden down with cargo. So it's arguably more of use as a combat vessel in conflict zones and resource extraction sites. Provided that the shield strength isn't nerfed too badly when the 1.3 patch gets rolled out, it should be a good ship to take down top tier Anacondas with for Assassination missions, too - at least until you can afford a Vulture.
Why you should ditch it: At the time of writing, the Courier does have a couple of major problems. The FSD range is pitiful if you're intending to use the ship as a courier for faction missions and the ship is almost impossible to refuel from stars without taking heat damage. I'm assuming at this point that it's a bug that may get addressed before release, because currently, you start taking heat damage in around 10 seconds, unless you're right at the edge of a star's atmosphere, which slows down the scooping rate to a crawl. It's also relatively expensive, given that you can get twice the cargo capacity, more hyperspace range and an almost equivalent amount of combat power out of a Cobra. So you're really paying a premium for that third medium hardpoint. It appears that the Courier is intended to be a stopgap ship between the Viper and the Vulture in the combat-aligned professions, but it's hard to justify the extra cost, even given the Courier's amazing shield strength.
Lakon Diamondback Scout (DBS)
Cost: 564,300 Cr
Recommended weapon loadout 1 ("Combat" Explorer/Scout): x2 Class 2 Gimballed Pulse Lasers, x2 Class 1 Gimballed Burst Lasers
Recommended weapon loadout 2 ("Pure" Explorer): None!
Recommended weapon loadout 3 (Interdick): x2 Class 2 Gimballed Pulse Lasers, x2 Class 1 Gimballed Multicannon
Why you should fly it: "The Flea", as it has been affectionately nicknamed by the G+ community, is a poor man's Asp, or perhaps a rich man's Cobra, depending upon which way you want to look at it. The Diamondback is billed as a long range scouting vessel, or "combat explorer", which is a sure sign from Frontier Developments that the business of exploring may be about to become a whole lot more dangerous. Given that most explorers fly without shields or weapons and strip down their thrusters and power distributor to save mass, if the Thargoids do rear their chitinous, insectoid heads, there might very well be a slew of casualties amongst the more adventurous Commanders in the Elite: Dangerous community. With a long-range combat spec (i.e. laser weapons only), the Diamondback does give you an equivalent combat power to the Cobra, but has a slightly better hyperspace range. The weapon hardpoints on the Diamondback (as you'll see below) are well-placed to give you much more of an opportunity to bring all four of your weapons to bear on a target simultaneously, compared to a Cobra or Viper. The Diamondback is also more agile than either of those two ships, meaning that it's also a passable bounty hunter (against smaller ships) in RES combat. Being a Lakon ship, the cockpit view is great for both exploring and combat (something it has in common with the Courier, in fact), but the Diamondback is by far the best Lakon ship for battle, given that it's smaller and so much more maneouvrable than the Asp. Out of the two ships introduced in the Powerplay update, I'm of the opinion that this is the pick of the two of them. It has greater range and a similar combat power to the Courier for only a quarter of the cost. It's a viable alternative to the Cobra as both a combat ship and as a stopgap between the Adder and Asp in terms of exploration. It's good fun to fly, can hold its own in combat, and has a decent reach in terms of its hyperspace range. If you want a cheap, but robust ship to explore the hinterlands with that will give you a great panoramic view from the cockpit, then the Diamondback is your girl. I can see it being very popular with commanders that want a secondary ship for exploring that doesn't require the massive credit investment of a dedicated explorer ship, like an Asp. Another possible role that the Diamondback could be suited for is that of an Interdick - that is, an Interdiction Bounty Hunter. In 1.3, assassination targets will not just appear in Unidentified Signal Sources, but will also randomly spawn in the systems highlighted in the mission parameters, allowing you to hunt them down in SuperCruise. The Diamondback's good FSD jump range and fuel tank capacity means that you can put the ship's four utility hardpoints to good use, allowing you to scan and hunt down anyone who tried to flee from your wrath. The Diamondback is one of the smallest ships to give you this much flexibility with your utility options, so is a good ship for this kind of role.
Why you should ditch it: Even with a "pure" explorer specification, the Diamondback will only give you an FSD range of around 27.5ly, which isn't really that much of an improvement over what you can get from an Explori-Hauler. So the Asp is still the best option when it comes to giving you the best FSD range for your credits, and the Asp is far more versatile, thanks to its configuration of internal compartments. Like the Hauler, the Diamondback only has four internal compartments, which isn't really enough if you want to create an explorer-class vessel that still has a chance of survival in combat. You have to choose between either the security of a shield generator or the extra income potential of a detailed surface scanner, unless you're staying close enough to the Old Worlds that you don't need to fit an auto field-maintenance unit. One thing that the Diamondback is also singularly unsuited for is cargo hauling. A Cobra is a cheaper option, able to haul more than double the cargo of a Diamondback, and is arguably more robust in a fight, too. The Diamondback isn't a ship that's going to earn you a fortune, via any means, be they combat, trading or exploration, but it does fit a hitherto unfilled niche in the ship market. It's a good ship for new players on their way to bigger and better things, but for most people, I think that the Diamondback is going to be a secondary "leisure" ship to fly when you want to take a break from your primary game role.
Lakon Diamondback Explorer (DBX)
Cost: 1,635,691 Cr
Recommended weapon loadout 1 ("Pure" Explorer): None!
Recommended weapon loadout 2: (Thargoid Hunter) x1 Class 3 Gimballed Beam Laser, x2 Class 2 Gimballed Pulse Laser
Recommended weapon loadout 3 (Combateer): x1 Class 3 Gimballed Beam Laser, x2 Class 2 Gimballed Cannons
Why you should fly it: The biggest problem with the Scout, as an exploration vessel, is the lack of space in its internal compartments. The Explorer goes a long way to addressing this, but is still rather skinny on internal space for true, long-range exploring beyond the galactic centre. It should see you to Sag A* and back, provided you're careful, but the ship could really do with a larger fuel scoop. However, it is a lot cheaper than an Asp, so I guess you get what you pay for. The DBX does have the hyperspace range to reach the parts of the galaxy lesser ships cannot reach (i.e. requiring a 30ly jump range), so it is a good option for your first serious forays into the deeper parts of the galaxy. It's also quite handy in a fight, too. The DBX gives you the cheapest access to a Class 3 weapon hardpoint, so as a combat explorer (a.k.a. Thargoid Hunter), the DBX gives you better range than a fully-kitted Asp and better firepower against big ships, as well. You can do a surprising amount of damage with one in a RES too, so as long as you don't want to haul cargo, the DBX is a pretty decent multi-role ship, at a price that won't break the bank.
Why you should ditch it: The Diamondback Explorer is a multi-tasker. I describe multi-tasking as doing several things at once, badly. It's not quite a great explorer ship and it's not quite a great combat ship, either. It's not terrible. It's not a waste of space like the Federal Dropship is, for example, but it is clearly going to be either a stopgap ship, or a leisure ship you bring out every now and again for some fun in a RES. The lack of internal compartment space means that as soon as you can afford one, you'll want an Asp for exploring. The low shield strength means that you're going to want to switch up to a Vulture as soon as you can afford one of those, too. The jump range of the Diamondbacks does mean that it's going to be a desireable ship in the early game for new commanders, but once you've gotten a few months of flying and a few dozen million in your Bank of Zaonce account, the DBX is a ship that will inevitably get parked for something bigger and better.