I'm with DN...

It's 4x5 about 75% of the time, and 8x10 almost the rest. I do some 6x7 when I travel for work to places where I really can't be lugging a bigger bag and a tripod.

I used to have a 5x7 and I miss it. Now that I am contact printing and using Azo I realize how much I love that format. It's big enough for serious contacting, but no heavier than a 4x5 kit, and I actually like the longer rectangle because it feels like the 35mm I "grew up" on.