I still have this one and probably will play it again at some point. The last time I pulled it out must be a couple of years ago by now, though.
I've played all the different races quite a bit, but I usually wind up going for the Romulans. I think the Romulans and the Ferengi are definitely the easiest races to play. The Ferengi have a weaker military, but it's not too bad, and their economic/diplomatic advantage with the trade routes is massive. The Romulans are the only real Jack of all Trades option who aren't super amazing at anything but also aren't at all bad at anything, and they get the cloaking devices to boot so you never have to lose a ship to an unavoidable battle.
By comparison, the Federation diplomatic advantage is ok, not great, and their scientific advantage only matters in a *really* long game (but I do love the Heavy Escorts when a game lasts long enough to bring them out). Meanwhile, their 'morality' outlook is incredibly frustrating. I remember one game where one of the minor races (I think Talarians, but I'm not sure) who I had done absolutely nothing to just kept attacking me out of nowhere. Their ships would be destroyed in self-defense and I would immediately ask for a peace treaty and still everyone was constantly whining about the 'war'. After like the fifth time they unilaterally declared war for no reason, I captured the planet and put a stop to it, and people rioted in response. It was utterly ridiculous.
Then there's the Cardassians who basically feel like the game's built-in 'hard mode'. Not really great at anything and also you have to start at like three steps lower down the technological chain than everyone else.
But the Klingons are unquestionably the worst option in the game. Their 'morality' stuff can be almost as bad as the Federation since they'll sometimes start rioting just because you made peace with someone. And that Dilithium deficiency is an absolute killer. If you don't get lucky enough to have at least 2/3 new dilithium rich systems near enough to colonize/conquer in the early game you're forced to spend the entire game struggling to keep any fleet in the air at all.