I am a rightie, but I usually like to stand southpaw.
I say usually because if all I am doing is boxing then I stand orthodox. Why? Because while my left hand is much quicker and has a much better jab no matter how much I work my right to the contrary, the exact opposite is true with my legs. My left leg is twice as strong, agile and fast as my right when throwing kicks. So when kicking is allowed I switch back to southpaw because I would much rather have fast and devastating kicks.