I am between a 36 and 38, a small C cup.  I ordered the 36 and it made my breasts look so sad, nipples just barely peeking oddly over the cup.  It also caused the unattractive "back fat" look that I don't usually have.  The straps were not long enough to adjust to fit well.  I don't think ordering a bigger size would help; I think the cut is simply not flattering for me.