If I had to pare down to a single pistol, the one that I'd keep would be my Glock29 as long as I wasn't forced to give up the spare barrels at the same time. 10mm is nice, but the ability to swap the barrel and go to .40S&W is proving nice for the pocketbook factor and convenience of not always chasing brass. Add in the fact that I can use the G20 Mags as well with an adapter to make a full size grip... It's a nice combination. Ugly, but shoots nice and has done everything that I've asked without complaint.
I love my Colt, but it wouldn't necessarily be my go-to gun these days. It's prettier than the glock and lots of fun to shoot, but has expressed marked ammo preferences.
The SIG P229....nice gun, but it just doesn't speak to me. It would be first on the chopping block.
Now my wife has expressed interest in acquiring a Ruger SR(x)c or a G26/27. She likes the 9mm, but it'd be quite convenient if she would step up to the .40. I'm partial to the idea of only needing to stock .40 in quantity.
Granted, thinking about it, twin G27s might be even better for the house than a G29 + G27/Ruger SR40c combo... 1 caliber, one set of mags, parts, etc... The big boom from the 29 with a full load is lots of fun though 
But given that' you're all 9mm, I'd try a G26 out and see how it feels.