In a particular game I picked vampires claws and also obtained vorticular cutlasses from an ARS - so was able to do a short comparison study of the two. These melee ship-types definitely require regular replenishing after a heavy engagement, so I'd treat them as something of a generic force-multiplier (zenith viral shredders multiply themselves for you, so you shouldn't need to ever build them more than once.
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The main advantage to getting melee ships is that they're immune to both tractors and forcefields. Note forcefields, since you'll be able to kill annoying ships hiding under them: ion cannons, counter-spies especially. Mass-drivers, guardposts, and starships are generally immune to fusion cutters, so cutlasses are the best for this job. Vampire claws and shredders are more creatures of fleet-battles.
Aside from the wider variety of attackable targets, you'll also get more offensive bang from cutlasses due to a higher ship-cap (200, althoguh less than a good sized shredder force). Just keep building them to counter the high attrition rate.
Vampire claws are oriented as hunters and work more defensively. They are 108-speed on normal compared to cutlass's and shredder's 52, more of a utility ship to take down enemy fleet ships you don't want hanging around. These last longer as a 60-cap fleet than the 200-cap cutlasses (of course, since cutlasses hurt themselves and vampires do not), and the critical difference is that you *can* use these to catch bombards and snipers.
Unfortunately, in the overall comparison blade s'pwners are better because they spawn for free, and fly much faster than everybody else.
SummaryVorticular cutlasses: Upsides are blade damage can kill things which are immune to fusion cutters, like guardposts and starships - can snipe these things under forcefields for the player. Downsides are high attrition rates, and build slower than fighters despite double-cap. Outclassed by spire blade spawners in this field.
Vampire: Upsides are high-speed (108, just slightly faster than raiders and equal to space-planes). Will last a long time if you can keep it fed in battle. Note 3x polycrystal bonus. Downsides are also attrition rates, but you'll build a cap of these in the same time you can build fighters. Again outclassed by spire blade spawners in this field.
Zenith Viral shredders: Probably the main reason you'd ever crack open any zenith cache lower than mark IV. They replicate for you, and would be better than cutlasses if not for its fusion-cutter damage type. You'll have slightly more than twice the cap per mark when well-maintained. Downsides: The zenith caches mean that you don't
really need to unlock these as a starting bonus.