Swimming nude is the best way. If I have to wear something, the smaller it is the better! I have had to wear a thong on a beach but removed it when in the water so I could be nude. Only reluctantly put it back on wading back into the shallows, Swim nude!
Swimming naked is the only way to swim. Once you have done it you feel offended when you have to to wear swimsuit . I used to wear underwear gave that up two years ago.
I sometimes wear underwear as outer wear. A pair of bikini briefs will keep me legal when the heat and humidity are too much to bear, and a pair of sports briefs serve as a swim suit when one is required.
I didn't think swimming nude would be any different, until I tried it. It feels great! Last time I swam nude was in the sea. My wife an I went did a short bush-walk and ended up at a small secluded beach. We didn't bring swimmers or towels because this walk wasn't our original plan. However the water looked so inviting so I just stripped off and went for a swim. My wife was too shy, so stayed clothed on the beach. The best thing was just getting out and walking nude on the beach and sitting on rocks until the sun dried me.
I have tried going sans-underwear and find it works only occasionally in jeans but not dress pants for me; just not my thing. I do have one swimsuit for when I need to wear it, but the need has to be there because I really don't like it. If I can swim without anything at all that is defiantly my choice.