I agree about k414. It's on the easier side of difficult. And so beautiful! the development section in the first mvt....

Perhaps worth knowing is that concertos nr 1-6 is not original compositions, it's arrangements he did to study concerto-composition. (Please correct me if I'm wrong!)
Nr 9 is considered his first "great" one.
Nr 11-13 (K413-416) are with wind instrument 'ad-lib', i.e he composed them so that you can perform them with strings (string quartet for ex.) only.
nr 14-27, immortal miracles!:-)