i would say both are equally reliable. A better question would be which will work better for your carry style. Sigs I have seen with a tendency to rust moreso than the glocks, especially down here when carried on a sweaty body. i am a fan of the glocks, but i wouldn't kick a Sig out my holster either.
Sigs are generally heavier.
Depending on model, less rounds for a bigger gun.
More expensive.