My LO wears a tankini. I don't like her to wear her swim diaper there in case she pees on the way so I'll put her top on and change her bottoms when I get there. There's always someone waiting for the family bathroom so I don't like to take too long. It's also convenient if I have to change her during class (which I haven't had to do yet). But the top will ride up sometimes.

If she were in a one piece the top couldn't ride up, but then I'd have a tougher time changing her.