i've found it really doesn't matter what you use, just build what you need to keep from getting your a** handed to you till you can research up to "Returning Aramda".
then you really have nothing to worry about since that will auto spawn a large overwhelming force to all of the planets you hold,then you can just planet hop after you form a fleet and gather your forces in one place, and overwhelm and out gun just about anything you come across.
Save for a high population of pirates, i tried to take out a pirate base the other night on single player after the AI wussed out and quit when i took it's capital planet. UGH forget it no matter how many ships i sent to that damn planet i always got rolled