Both - but if you do both, practice both. Different draw length (feel) when sitting than standing.

Took my biggest ten point two years ago while sitting.

Also, when practicing, make sure you do different things, such as crouching, leaning and odd twist angles. I have a platform nailed up in a tree in my backyard. Kind of a pain in the butt climbing up and down when practicing, but hey, that excercise is good :-)