Thats a loaded question!
We'll do a quick break down of what suits work in what temperatures for Surfing whether you're in British Columbia, Quebec or Nova Scotia. As temperatures get colder you can also add an accessory like the Isurus Alpha Ti Hood
2mm - Summertime suits for temperatures over 18 degrees Celsius
3mm - Spring/Summer suits for temperatures in the 13-18 degrees Celsius range
4mm - Spring/Fall Suits for temperatures in the 10-15 degrees Celsius range
5mm - Fall/Winter suits for temperatures in the 3-10 degrees Celsius range
6mm - Winter Suits for the harshest temperatures, watch for ice in the water!
As the suits neoprene thicker you get less mobility and flexibility in them. Thats why we only carry suits that use Japanese Limestone Neoprene in them. They hold less water, stay more flexible, are environmentally friendly and keep you warmer.
And don't forget your Booties and Gloves