My glock 17 mags fit the same kydex mag pouches I use for my CZ75, BHP and other double stack 9s...
The Glock 17 is great for all the reasons listed above, and would be my recommendation.
I've used my friends M&P and XDM... The M&P trigger is GARBAGE, and needs an Apex kit, taking the cost to Glock prices. IMHO the XDM is goofy looking... Too plasticky with texture all over. It does shoot GREAT though. Problem is accessories... Pretty much are none. He can't even find spare mags for the XDM, though you can get them if you buy the XD.
I've not shot the Ruger, but I've never been impressed by their semis.
You have the same problem with accessories and aesthetics, but the Steyr and Walthers get good reviews. I've not shot them either.
Do you have a local range that loans pistols you can test fire?
IMHO: you'll probably wind up back at the Glock as it is good (if not great) in all departments, and tons of parts and accessories are available for it...