The Sigs are outstanding weapons. My wife shoots a sig better than a Glock, by far, for some reason. I don't.
I'll say a few things... If you are going to put a LOT of rounds throught the gun, the Glock is the way to go. Less maintenance/repair required per 1000 rounds, and easier to get worked on (more plentiful glock armorers). The Sig is very popular with the Navy SEALs, but they have their own armorers. The Sig trigger after the 1st shot is xlnt. I find the high bore axis of the Sig causes more muzzle flip, but in my hand, there are few guns more comfortable than the Sig.
Shoot 'em both... you'll know.
PS: I'm adding this after reading posts below... my personal vote is with the Glock 19, my most-carried gun. Best compromise between size, wt, sight radius, capacity, etc. And of course, extremely reliable. Try one, and you might love it.
[This message has been edited by Covert Mission (edited August 07, 2000).]