True to size -- REAL size, not by squeezing to get into it. I'm a small 26W, and I ordered the 4W (26W-28W). It goes on easily. I'll end up having to take the straps in a little as I lose weight from swimming, but it fits well (including my 42G cup size) and looks good (straps don't dig in either). With strap adjustment, I think it will even work until I fit into my size 20W suit. The krinkle fabric gives it a little style.

The only people who might have trouble with the fit are those with very small shoulders or "petite" cup size.