i have both-full suit bare 7mm for water 50* and up
2pc brand x for 32*- 50*
as boat sju said: more neoprene around your groin....
dry suit if i'm in for a couple dives,or no shelter to change out in
have fun
yaeg
OK, here's the deal - Listen to us old guys with hundreds of cold dives and not to the ones with under 100.
Yaeger is telling you, as some of the other old guys are, the facts.
I have 7mm 1 piece suits, 2 piece farmer johns, hoods and hooded vests.
I also have tropical suits with which I also take along a hood (for a little more warmth) or a 3 ml tropical hooded vest. It makes things very flexible
A 2 piece farmer john is warmer that a 1 piece -duh!!! You have 7mm all over your whole self, with an extra 7mm (= 14mm) over your torso and groin.
-------But, just as the sages have said, you must get a cold water hood (a hood with much longer flaps. That is what I have and no water goes down the back.
A one piece isn't as warm, but a one piece with an attached hood is warmer than a 1 piece.
However, a hooded vest will warm anything up. Put a hooded vest under a farmer john or under a one piece and now each is a step up in warmth than what it was before.
My O'Neil 7mm Farmer John with a cold water hood is so incredibly warm. If I put a hooded vest under it, instead of the hood, it is actually too warm to dive 46f degree water! So I don't dive it with a hooded vest. But my face, around my mask, is stinging with the cold.
I also have a lovely ScubaPro TeK 7mm 1 piece which offers some real flexibility. Put on either a cold water hood or a hooded vest and it's pretty warm. But it comes with a different kind of vest as well - a step in, zip up the front, w/o sleeves. If you put the hooded vest under this, you will feel like the michelin tire guy, but warm warm warm. Personally, if I wear it with the vest - the cold water hood is plenty warm.
I have dived dry. I don't like it and won't do it. I Jetty dive - too many places for seals and valves to get destroyed and, unlike my drysuit friends, I have never had to call a dive because of "suit failure". Also, I'm OK with the warmth of the wetsuit. However, if I was diving 45f degrees and colder from boat or a bank (not from "suit ripping Jetties), or that National Geographic guy with the leopard seal, I would get a drysuit. And I wouldn't look for the cheapest - $1,000 - $2,000 -$3,000. Also, deep tech requires a drysuit.
Over the years, if you stay with diving, you will have your collection of equipment. One size doesn't fit all and you won't necessarily get it right the first time. The most important thing about any piece of equipment is what is best for you - and proper fit is what makes the difference with any wetsuit.