Rhonda, I prefer 11x14s for my never-leave-home-without-it portfolio; it's an excellent 'show & tell' size. It's also a great size for art walks (where most people don't want to lug anything too huge around) and to hang in cafes and coffeshops -- usually matted to 16x20, but sometimes not.
Of course I sell much larger, and much smaller, and everything in-between. But, in the real world, I definitely consider 11x14 my go-to size. It's an especially popular size for series and sets (multiples).