Hi--not a dumb question, but one that has an individual answer, I suppose.

I never wear a swimming suit during a tri, because I always wear a running bra. So if I can wear a wet suit, I wear my tri shorts and the bra under the wet suit. Otherwise, I wear a Sugoi trisuit, which is essentially tri shorts with an attached top. So I do the whole thing in the tri shorts only, always commando.

My experience is that tri shorts are bike shorts with less padding. Dries faster, easier to run with. Doesn't give as much padding on the bike. I'll be interested to hear what others say.