Two piece, preferably a halterneck.
Buying the perfect bikini truly is a chore though. I need specified cup sizes, no S, M L BS where the cup size and the overall size of the piece go hand in hand, I'm not made that way. I got lingerie for-me-for-hubby last Xmas, and just like most bathing suits lingerie generally comes in moronic sizes from extra small to extra extra large. Fun to buy something new and expensive 3 sizes bigger than you actually need and then have to get the sewing machine out and take it in several inches everywhere just so the boobs will fit *growl* The sales people at Victoria's Secret suggested getting a size inbetween so nothing would fit right. Great... *grrr*

And I like under wires and NO PADDING, padding makes me feel Dolly Partonesque'r than normal and I makes me slouch and feel very uncomfortable.
/end of rant