Raptors - you might not see much that's unique just looking at their stats, unless you notice their speed. Their ability to "kite" the enemy is unparalleled, and can lead to wildly different tactics.
These I'm not sure what to think, they seem like a jack of all trades master of none, their most pronounced trait is their speed, but speed is mostly best in some sort of raiding, if they ever have to tag along with the main fleet their speed is not much use in my experience. Then they cost an enourmous amount of metal which almost forces you to choose between them and bombers unless you wish to wait years for your fleet to fully build. In the end with their range, dps, speed and low life they could be a form of skirmisher in early game but as soon as you hit your first tractorbeam then they lose all functionality. Seeing as they cant be sent in first to soften up the defence and if the main fleet already has entered the system then the enemy tends to ignore them and focus on the main fleet.
Tanks - sure, these can be somewhat similar to bombers in function broadly-speaking, but because of the high shielding of these guys they can get where bombers sometimes can't.
Thats assuming that you need your bombers to get somewhere without cover from your fleet, which in my experience is a suicidal waste of resources (diff 7), I dont recall ever having meet a target to tough for a cheap raiding unit to kill and at the same time not being a goal for the entire fleet to simply attack.
Parasites - capturing ships from the enemy to use for yourself? Awesome.
Their reclamation is cool yea, but their biggest problem is they cant mark ships for reclamation, it only happens if they kill it, which is hard if they follow the main fleet seeing as they dont have a significant damage output. A single Leech starship is easily better than a horde of these simply because it can mark 40+ ships for reclamation on every shot.
Paralyzers - great for delaying the ingresses of big waves, or particularly big ships. Nothing else can really do that to the same degree.
I've never gotten these or Viral shredders in a mapseed before, after I saw your reply i even tried to make 10 new mapseeds without luck, how do i get these as start ships?
Raiders - sure, these might look similar to fighters or similar at first. But the ability to get past tractor beams unscathed is pretty amazingly useful and really makes these guys feel very different.
These I really dont understand. Yes they are immune to tractor beams BUT they have shit for life 8k at mark 1 if i remember correctly, and they cost alot of resources 300/300 for mark 1. For the same price I could get 6 Autocannons which had significant more life, double the speed and invisibility. Yes Autocannons can be tractorbeamed but i can built 1000 autocannons for the same price of 150-200 raiders of same mark which will give me enourmous amount of ships to sacrafice to tractorbeams while moving invisible to my mark.
Planes - similar to raiders in some respects, but weaker and with cloaking. This makes them better at striking from cover, if you put them in low-power mode until they reach their target.
These I had not encountered before, but with significantly increases attack, reduces building cost and added invisibility I can see how these are excellent raiders, but besides having a little more shitty life (5k difference at mark 1) they are superior to Raiders in every way, which brings me back to what is the Raiders function? Yes the life difference is more pronounced at later mark lvls, but at later planets theres so much defence the raiders are going to be dead long before they reach their target anyway.
Viral shredders - a von neumann (sp?) machine, in essence.
And so on and so forth. Every ship has a niche of its own, and is useful in various situations. Maybe snipers not so much at the moment (we're always tuning the balance with feedback from folks).
Hope that helps!
But I suppose in the end its a matter of opinion.