For casual wear or water exercise, two-piece suits and one-piece, scoop-back suits are fine. For lap swimming, one-piece racer-back suits are best.
Suits should fit snugly but not too tightly. If the straps dig into your shoulders, try a larger size. If you see extra folds or wrinkles of fabric on the torso, try a size smaller. Here are the basic options:
One-Piece Suits—Racer-back suits will allow your shoulders optimal freedom of movement and will ensure the straps won't slip or fall down while you're swimming. Some suits offer a more modest leg cut.
Two-Piece Suits—These work well for casual wear, water exercise and beach sports. Some feature a cropped top, while others have a longer tank to cover the torso. Because they're not as streamlined as one-piece suits, they're not best for lap swimming.
Legsuits—These full-body suits have a high neck and cover the thighs for less resistance and drag in the water.