Edit, having almost finished a 60-planet game with a buddy (we've been playing since september) and just having a core world left, here are revised ratings (pretty much completely revised, btw):
Top Tier:
Raid Starships - these are excellent for dealing with lightning turrets and electric shuttles, and raiding.
Raptors - excellent quick response unit, with a long range so they can take on electric shuttles.
Electric shuttles - the bane of my existence in the hands of the AI, these will completely decimate an entire blob of ships. Less effective in player hands because the AI doesn't bunch up as much, but still extremely useful vs waves / CPAs.
Mobile Repair Stations - I like fixing my units rather than having to build new ones or maintain engineer fleets.
Scout MK III - with a full cap of these guys, I've been able to scout out virtually the whole galaxy on a 60-planet map.
Mixed Bag:
Laser Gatling - more useful in the early game than later on, as they die in droves and are only about as fast as fighters.
Parasite, Leech Starships - Getting free units for killing AI dudes? Yes please. Of course, they're not nearly as effective nowadays with all the "recent" nerfing, but still.
Space Planes - despite their silly name and weakness, they're actually pretty effective in a quick response role, supplementing raptors.
Bombers, Fighters, Cruisers, Basic Turrets, MLRS Turrets, Missile Turrets, Tractor Turrets - these have their strengths and weaknesses, and I'm happy having them in my force.
Autocannon Minipod - When the AI brings a few hundred mark IV minipods to your systems, runs them past your defenses and starts blowing up your mining facilities, they're pretty effective. When you're just relying on twenty reclaimed mark IIs, they're not very effective.
Bottom Tier:
Sniper Turrets - Initially, when I saw these, I thought "Oh no, the bad guys are shooting at me from across the map, my fleet is going to die so I better take these out quick." Turns out, you can pretty much just ignore them. On defense, since you get them unlocked right off the bat anyway, they'll help you lock down one or two systems at most before you run out of cap.
Space Tanks - Too slow to get to the AI systems in a timely fashion, and only mildly useful on defense as the AI will often not stand and fight, but rather just spread out through your system and blow up mining facilities. I guess if you need to use your resources for something, you can build these.