I dive in cold water almost all year long. Even under the ice. The first thing to stress is always, and I mean always, choose an attached hood. Whether you decide on a full wet suit with vest or a farmer john with a jacket, the one sure fire way to get cold is to have water bleed in through the neck seal. With an attached hood, this is far less likely to happen. Secondly, wet wuits with zippers at the ankles may be easier to get into, but they will also leak water up your legs easier. If you can handle a little cold on your legs, don't worry about it. If you are sensitive to the cold, avoid the zippered ankle variety. Now for your feet. Most people will spend time on looking for a good wet suit for cold water, and then give the feet a mere glance. Don't do this. Choose a good pair of boots, and use a pair of 2mm neoprene socks under those 5mm boots. Some people use wool socks, and it does help, but the neoprene socks are by far the best.
Of course the warmest is still a dry suit, but only if you can afford it. I still use a wet suit, and just purchased an new set. For what it's worth, after trying a few different makes and models of wet suits in 38 f water (4 c). I settle on a 7mm Mares with the 5mm overshorty with attached hood. Mmmmm warm. That silver something or other lining they call Z Heat seems to work.