I recommend Xterra wetsuits. They are almost always on sale. I hate being cold. Iâ€ve done several miles in the Pacific during the winter and theyâ€ve really been comfortable.
Yes, I swim in open water with a long sleeve wetsuit in the early spring, and late fall. Ideally the suit (arms and legs) should fit in such a manner that they're tight...and thereby won't let 'a lot' of water stay in them. Really just a very thin 'layer.' But remember...part of a wetsuit's effectiveness is achieved by water actually being inside of it, warming up, and providing additional insulation against the cold. Most open water swimmers (i.e. triathletes) find that with the right wetsuit they swim faster. That has never been the case for me. It seems that I swim, at best, the same speed as without the wetsuit.
Dan