The Glock 20 is probably one of my favorites. Mine is magnaported, which I really like. If you're into reloading, then you'll find it's about the same cost to shoot 10mm as .40 S&W.
A good conversion barrel to .40 S&W isn't a bad idea, either. The G20 is softer shooting then other Glock .40 S&W pistols thanks to it's heavier weight.
I had reliability problems with a G20 Lone Wolf barrel, so my advice is spend the extra money and get a KKM, mine has been 100%. 10mm magazines will feed and function with .40 S&W or .357 Sig ammo. I use a different spring for .40 S&W, but that's not necessary for all loads.