bige, you do realize that the olde 6 shooter revolver is the most reliable gun on the market. I understand you would want a modern day semi but a revolver has a less likely chance of ever malfunctioning, not saying it can't happen but it is just less likely to compared to a semi.
Now, back to your original question. Glock is probably the most widely carried firearm by the police units. However, some do carry the Sig P226, which is a beast of a gun if you have the money.
I would suggest you go shoot all the guns you mentioned, S&W, Xdm, Glock, SIg and see which one fits your hand and shoots the best for you. However, if I was going to list the guns based upon my preference it would be: 1. Sig P226, Xdm, Glock, then S&W. But hey that is just what I like based upon my experience which each.
Good luck & Keep us posted