I am a huge glock fan. Though I just sold mine to buy an M&P because I wanted something easier to carry since the G30sf (compact .45 acp was so dang thick). I shot the first batch of Sigmas and didnt care for it at all.
Would I buy one over a glock? Probably not due to just the fact I still dont completely trust it yet. And I dont care for the looks of the sigma. Am I saying it is a bad gun? No I would just have to shoot it and give it time. Would I buy one? Yes, but I want something proven reliable for carry.
Now I have had great results with Glock and Ruger (for that matter) customer service. I am sure S&W is great. But having only a old .38 special and .380 I never needed them or anything. And with the addition of my new M&P I am hoping I wont need them for it either. Called glock for some replacement parts to put back in my gun toolbox kit. Ruger was for a new grip. I can make a list of pros and cons for the Sigma as well as any other gun.
BTW I never had to "re-learn" to shoot when I picked up any glock. Had three Rugers (2 p89s, 1 p90) a small beretta, small luger, a .357 ruger, S&W .38 special, S&W.380. And shot the M&P, XD, and a HK USP before purchasing my glock. Still never had to adjust. I know alot of people say they had to. My friend says he has to hold his head funny to aim. I never had a problem.
If Sigma proves to be reliable and the cost stays down the heck yeah I will get one. My biggest turn off really is the experience with the first one I shot awhile back. Second is the looks. Though the solid black isnt as bad as the steel color slide.