I do mostly 35mm and my equipment limits me at 11x14, so I settled down on both 8x10 and 11x14 (sometimes cropped if the neg is worth printing full frame). 8x10 for me is the print-in-hand size, it allows me to decide whether something blows or not, and is large enough for wall display in my house.
When I sell prints or exhibit, I do 11x14 for the extra size, and because it makes things more easy to see from a distance. Surprisingly, nobody bought 8x10 at my april exhibit. I only sold 5x7 or 11x14.