Hmm, I’m at heart a prosaic soul and I can’t now help thinking how impractical a swimsuit under armour would be for … erm … wild toileting. You’d need to more or less completely strip if you needed a wee. Though now I come think of it, perhaps it has some sort of buttoning down below, but then that would need to be carefully designed so as to not chafe and also not be dangerously fiddly. Of course, this is a fantasy adventure and we don’t really need to worry about such stuff, but I just can’t avoid it when presented with something that seems such a bad idea from a practical point of view!
Though I’ll admit I’m in the camp that generally hardly ever sees and pretty much never thinks about their characters’ underwear, so almost anything is okay for me really. I have a slight preference for underwear for both male and female characters that looks at least vaguely practical and appropriate to the time and place, but that’s it.