Regardless of the make or model of graphics card, every LCD/LED monitor has a "Native Resolution" which is specified in the user manual. This gives the sharpest and "perfect fit" image for that size screen, and it should therefore be set to that resolution in Windows' display settings.
A 21.5" or 22" monitor usually has a native resolution of 1920 x 1080 so that's what you should set it at.