Definitely one-piece, and I am most comfortable in racing suits (this preference may come from the years on swim team, plus a lot of other suits have extraneous ruffles etc. or aren't cut in a way that they stay in place). Who wants to have to worry about a "wardrobe malfunction" if she decides to jump or dive into the pool/lake, bodysurf at the beach, etc.? I've never liked bikinis anyway, just don't feel comfortable showing that much skin.