Out of the two, I've only shot a buddy's 9mm sigma. It was a nice shooter, but that is the extent of my experience with it. My dad just retired from police work this past year, and while I went through my academy, I used one of his old sidearms. I don't remember if it was a 5906, or a 6906, but it was a 9mm compact. With that said, I wasn't very fond of it to begin with... I just thought it felt clunky, and even after shooting 2000-3000 rounds through it, I still feel that way, but I give it pretty good marks in reliability, and accuracy. I also tried a glock 17 while in the academy. I had always thought they looked like something that should be used in a driveby shooting, but after using them, I have a new found respect for their accuracy, reliability, and shootability(it's alot better than the s&w I was using). I bought a glock 22 the other day, so you know where I am putting my faith. I think it's up to you where you spend your money, try them all out if you can. I would think that if you were willing to spend the money on a sig, you might as well at least take a look at the glocks as well. Sorry about the rambling, and good luck in the search.
~~~Amos