I use an Elios custom. Just a simple, plain black, lined outside, open-cell inside two-piece wetsuit.
I can't tell you if it's warmer than others, I chose to spend a bit more from the start as I was done with mass-manufactured products failing on day three.
I can tell you however that where every shop around here on Crete adviced me to go for 5mm with their off-the-rack suits, the Elios keeps me plenty warm @ 3mm (16°C winter sea temperature).
Less neoprene means more mobility and less lead, so longer and more relaxed dives.
A big plus for custom suits is that you can choose the neoprene. Most off-the-racks won't state the neoprene used, and when I contacted companies (Seac, Cressi, ...) I either got no answer or something generic like "Taiwanese/Japanese". If they were proud about the quality materials used they would not just tell me, they would mention and advertise it everywhere.
I had mine made with Heiwa medium-density neoprene as it resists compression more for repeated deeper dives and generally lasts longer than the super flexible ones. Tbh I can't imagine neoprene being even more flexible than this. Perhaps this is different for thicker suits. But then again, better resistance to compression also means it keeps you warmer at depth.
The big downside of Elios is the shipping cost. From Italy to Greece it was around €40 in shipping iirc. The service (both the manufacturing and the shipping) was really fast though.