Gorgo said..
Depends on you, and the weather. Some guys wear boardies whenever the sun comes out. For me, the water might be warm but the wind chill can be bad.
I wear 3/2 when the temperature is in the low-mid 20s, 1.5mm to the 30's. If it's hotter than that then either a shorty or boardies and top. Whatever makes sense for the day.
I like to wear a wetsuit as sun protection so I might have a wettie on when others are riding in boardies. The other day I was wishing I had booties. The sand was burning hot so it was painful rigging and walking on the beach. I had to go back to the car and get some thongs.
Long leg short arm with rashie or neo top under wettie.
Next winter I'll be looking at Severne LL SS wettie to replace my old hacked wettie