Yes, fit is a major factor. If you can't get the undergarment in the suit you need you won't be warm. I would lean toward a custom fitted suit if you can afford it and if it's available from the manufacturer you choose. I started with a USIA (made near Portland, OR) I think it's more of a 2 ply but I was in hurry for a wreck class trip on Vancouver Island and took the suit off the shelf. It looks kinda bulky on me but it served me well. I now dive an Apollo (4mm neoprene) which I bought from a friend who lost a ton of weight and a great price. I really like this suit. It swims with less resistance and seems to be warmer for me. I got a diverite pocket glued onto it but I prefer the exhaust valves of the USIA better.
USIA
+ valves, boots (replacable), light weight, quick to dry, easy to patch, can have choice of zipper location (have been told one of the best is at waist where you can roll it up plus it's a self donning placement), plenty of room to gain weight(is that a plus?), requires less weight if you wear compressible insulating undergarments.
- baggy (depends on your body type and size), back air bubble, needed to wear gaitor to keep air out of the boots.
Apollo
+ less resistance swimming, slimmer fitting, warm.
- no pocket, exhaust valve is slow, when boots wear out you replace suit, neoprene will wear out and start to leak, maybe a little more weight required due to the uncontrolled air content of the neoprene suit material at the surface.
I'm neutral on the boot exhaust valves.
Just wanted to give you some more ideas on dry suit comparison that you may not be aware of. There are all sorts of options to each suit but highly dependent on the manufacturer and material chosen. I've seen some guys and gals really fill out the USIA and who would never get into an Apollo.
