We do both. I believe I am steadier seated since there is a better anchor point for my elbow, but it does hamper the range of motion and requires moving the tripod rather than walking around it. Most nights I hunt with a partner and that eliminates having to move the tripod as much when seated to position for a shot. We both scan with head mounted thermals, and being seated also limits that range of motion as well, but with two it works pretty well.
Over 50% moon and we try to set up with a background behind us to break our outlines whether standing or sitting.