Glocks and 1911's are my favorites. If you want 1911, then get it in 45. 1911's in other chamberings don't always work out as well, especailly 10mm. The Glock and S&W 1006 series were designed from the ground up as 10mm and are the only 2 semi's in that chambering that have proven up to the task.
What do you plan to do with it? For SD or range use a 45 is as good or better. My G-20 is my hiking/camping/outdoors gun. It serves that role well, and is where the 10mm really shines. I load mine with 200 gr DoubleTap ammo that I've chronographed at 1315 fps from my gun. That is about the same power level as the hottest 357 mag loads when fired from a 6" or longer barrel. The G-20 is about the same length as a 3" revolver and will easily beat 357 loads with barrels that short.
And it is closer to 44 mag than many realise, or will admit. Most of the magnum revolver loads you see published are from 8" test barrels. When fired from 3-4" barrels in real guns that people actually carrry they are not nearly as impressive. Double tap shows a 240 gr 44 mag load at 1500 fps, but when fired from a 3-4" barrel it MIGHT be at 1200 fps. Most standard factory 240 gr factory loads struggle to make 1,000 fps from 4" barrels in 44 mag.
A G-20 beside a 3" 629 for size comparison. The 44 from 3" barrels will be just slightly more powerful
http://s1129.photobucket.com/albums/m513/jmr40/?action=view¤t=001-11.jpg
A 240 gr 44 mag @ 950-1200 fps isn't that big a step up, if any, over a 200 gr bullet @1300 fps. If you choose to carry a 44 with a 6-8" barrel then you do have a big advantage, but I'd just as carry a rifle as an 8" handgun.
Don't let anyone tell you a Glock isn't accurate. If they do, what they really mean is that they have never developed the skills to shoot a Glock. A Glock is just as acccrate as a standard out of the box 1911. A 1911 can be made as a target gun with a slightly better trigger, but most standard out of hte box 1911's are no more accurate and have the same 5-6 lb trigger as a Glock.
Typical 50' Glock shooting.
http://s1129.photobucket.com/albums/m513/jmr40/?action=view¤t=001.jpg
The Glock 20's biggest disadvantage is the large grip that some just cannot handle. But if you already have a G-21 and are used to it then you won't have any problems. The wide, fat grip and grip angle of the Glock really spread out the recoil over a large portion of your hand. To me the Glock, even with the hottest loads is more comfortable than my 1911's in 45. The 1911's are heavier, but the narrow grip concentrates the recoil into a smaller portion of my hand. Neither are bad, and are certainly softer than magnum revolver recoil.