Originally Posted by immiketoo
Aside from what has been mentioned above(100% accurate BTW), the single biggest difference is the angle of the grip in relation to the slide. Glocks point high for me while Sigs point naturally. Sure, you can adjust and become competent with either, but I always go for the gun that feels the best while shooting. The difference in inherent accuracy of these guns is negligible.
This is a very good point. I forgot to mention the unique grip angle on the Glock, which is pretty much a love-it-or-hate-it feature of Glock pistols. Whether you like the style of grip on a gun (considering factors such as angle, thickness, length, texture, etc.) will most definitely play a role in how comfortable you are shooting that gun and subsequently, how well you can ultimately shoot the gun.
immiketoo makes another good point about accuracy. Glocks, Sigs, XDs, M&Ps, etc. are all inherently accurate, well-manufactured guns. The reason why you may be more accurate/proficient with one of these guns over the other boils down to the Indian, and not necessarily the bow.