Accuracy is not an issue that would concern me...but...
Keeping in mind that the G21 has an overly large grip for most average hands, I agree with the other recommendations here and to just mention to put some rounds downrange with one first and see how it goes.
Over the years I've run into a lot of folks that shoot my g19 or 1911 well that can't manage a g21 or will ever be comfortable with it, so it is not a workable choice for many shooters.
In the glock line-up, I find the G19-23 profile to be a good compromise. I am also confident when comparing the terminal performance of the 40 round relative to the 45...I generally have no issues with hot 9mm as well.
The Barnes all copper bullet raises the bar across all calibers, and tends to neutralize the caliber debate somewhat, but is certainly adequate by any standard of comparison.
Gripwise, G23 or 1911 is usually no problem for most folks.
