Talaras, I own both and the best I can tell you is that I have no problem carrying the 21 openly, however, it is heavier. More barrel for accuracy and more rounds in the magazine, but I'm a big guy (6'4", 225-lbs) so it doesn't even come close to uncomfortable and the larger grip is more comfortable for shooting. Absolutely nothing wrong with the 30, but it is smaller all around and can be concealed more easily. The 30 makes a great BUG to the 21.
“Malo periculosam, libertatem quam quietam servitutem." (I prefer the tumult of liberty to the quiet of servitude.). Thomas Jefferson
"All that is necessary for the triumph of evil is that good men do nothing."
-Edmund Burke, Loosely translated from Thoughts on the Cause of Present Discontents. (1770)