There's a ton in the mix. Springfield XD or XDm in .40, there's a compact model that's going to be a tad bigger, a tad heavier, and carry an extra round or two.
SW Shield is going to be smaller, it's single stack and it holds less rounds. It's not really in the same category as the rest on the list IMHO. I'm not saying it's bad, I'm just saying it's a different category. I'd add S&W M&P 40C to the list, roughly comparable to the Glock 27 but with more ambidextrous features and an accessory rail. I really like the M&P slide serrations.
Ruger SR pistols would have to be loved by Sir Mix-a-Lot, because they have big butts. The SR pistols have a manual safety (the Shield also comes with one, M&P compact has the option of coming with or without one), so whether you want the safety or not is up to you.
Glock 26/27 are pretty much the standard for the sub-compact double-stack pistols, but I believe the M&PC is an upgrade in almost every way...the only issue I have with M&Ps is the trigger, but you could get an APEX trigger to replace it.