Dont worry too much about the size thing hardman, used to work in a shop which sold heaps of wetties and every manufacturer are different. A good rule of thumb is that oneils are the biggest cuts followed by rip curl and peak with the really little ones coming out of quicksilver (why would americans make little wetties their all huge

). Not sure about the other manufacturers. A medium oneill is a large ripcurl or even an xtra large quicksilver. Dont forget about split sizes too if your short and fat get an LS suit its shorter in the body but wider in the shoulders (and gut) than L. Go to a good store with a big range cos there is always a suit that will fit.
Oneil suits are the best aswell (not just cos I fit them)