On the wall, I like the look of an 8x10 matted in an 11x14 frame or an 11x14 in a 16x20 frame.
In my current set-up going bigger than 11x14 is do-able but it would raise time/hassel factor of the printing session substantially. Not worth it.
Also, like most sufferers of this d*mned photography disease, I have a large excess of photographs and a severe shortage of wall space. Smaller prints are better.
Right now I'm printing 8x10 exclusively.