From GLOCK's website:
GLOCK "Safe Action Pistols"
The G20 is slightly longer (193mm vs 186mm) and wider (32.5mm vs 30.0mm) and taller (139mm vs 138) than the G22, so it is bigger, but only by a couple/few millimeters... we're talking fractions of an inch (25.4 millimeters in an inch, so 2.54 mm is 0.1 inches). Likely, you wouldn't notice the difference.
The best way to figure out which you like better is to get down to a range that rents guns and try both out.