While 9x12 is the most commonly used size, I have one massive problem with it, which is that no place that I've ever been too prints that size. They'll do 8x10 and 8x12, but no 9x12. Sorry, I don't do the online ordering thing, have yet to seen results that meet my standards yet from them, and the biggest issue is that it's by far too slow and if it dosn't come back to me the way I want, I'm screwed unless I want to wait another week to send it back, pay for the shipping to send it back, and then wait for another try. I know, not all are horrible but it's a time thing, I deal with deadlines that are at the latest 3 days total from the time of the shoot to post production and prints.
I know that I am one with beauty, And that my comrades are one. Let our souls be mountains, Let our spirtis be stars, Let our hearts be worlds.