For concealed carry,the 1911.All three are excellent pistols,but the USP and G21 are huge pistols,not easy to conceal well or carry concealed comfortably.
The G21 has a large grip,most folks find it too fat in the grip area,if you have hands that can fit well great.
The USP has a better grip in terms of size for most.
The 1911 is slim and most find the grip fits them well,while a full size 1911 is a large pistol,its not as large as the G21 or USP.The G21 and USP would be better for exposed carry or a uniformed officer with the proper holster and heavy duty belt to carry such a load.The G21 carries alot of rounds and this increases weight along with spare mags.1911 mags are slim and compact compared to the other two choices.I vote 1911.