This is an interesting thread, I like seeing how other people play. I do usually stick to one ship for quite a long time. When I do start picking up other ships, I most frontline-esque ship I will usually get and allow the AI to use is super high tech shield monsters, almost elusively tri-tacheon stuff. Other than that, I like fighter wings, big carriers, and long range stuff. I love fragile or risky, high power or fast ships, but I very rarely let the AI use them. Honestly the AI isn't THAT bad, but frankly its pretty much always worse than the player. The AI can manage support, carriers, and fighters pretty well with support, so I tend to stick with stuff like that. Also, if I pick up frigates, I like to leave them either in a big ball, or supporting something else.
When I play alone, or in small groups, I play super aggressively, but when I play with AI ships I usually just support them with whatever the hairiest destroyer I happen to have is. Playing alone is lots of fun, it really makes you feel like a bad ass. But, there are a lot of different fleet make ups you can do, and if you ride them hard enough to stop the AI from being stupid, you can make almost anything work, and I like that too.