Gunships for each race seem the most different - most cruisers and fighters are similar, but Gunships can be very different. Different weapons, speeds, and advantages for each kind...
Ishiman: Weapons are generally OK. They're relatively powerful, with a wide spread, but due to their energy base, they can run out kinda quickly. Shielding is durable - one of their advantages. Speed is the big disadvantage; these things are not very good to pilot unless your only other option is a Cruiser or Fighter. They're pretty good in groups and/or against big targets like Carriers. I think two by themselves (AI piloted) could kill any carrier except Salrillian or Audemedon - those short-range beams get 'em.
Cantharan: Only good at very short range - these things eat up cruisers pretty quick, and are good against big ships as well - but can be destroyed if attacked from behind. ("Prison shower" mean anything? ;)) Slow, OK shields, only short-range weapons.
Human: One of the better Gunships, and definitely the U.N.S.'s best ship. Rapid-fire, medium range autotargeting laser helps do a little damage, and is very good at revealing cloaked ships. The super-rapid-fire Magnetos are quite good, albeit short-range. Decent shielding, good speed (faster than Ish or Canth Gunships), very effective weapons. Extremely deadly in large groups.
Gaitori: This ship is fairly effective. It's actually faster than the Gaitori Cruiser, although with the same shielding (650) it's very easily destroyed. Nevertheless, the long-range homing pulse is very good, and the concussive pellets aren't bad either. If a good human pilot is steering this thing, as Pallas Athene said, these can be very good. The AI is okay but sometimes makes the Gunship vulnerable - it's obviously best at a distance. Fairly cost-effective in any number.
Salrilian: Very good ship. Good speed, cloaking field, plus very good shielding and good weapons make for a deadly ship. Long-range beams are very nice, plus the primary weapon is quite powerful. These ships are good by themselves or in groups of 2 or 3.
Audemedon: Possibly the best Gunship out there. Though speed is lacking, shields are very good and weapons are amazingly deadly. Just one or two of these can easily take out a small fleet of cruisers, or an Ishiman Carrier; in large groups they're absolutely invincible.
------------------
Joolzman5, that guy with the spikey red hair.
Those who say money is the root of all evil don't have any.
That lowdown scoundrel deserves to be kicked to death by a jackass and Im just the one to do it.