I'd say throwing velocity AND obvious athleticism will come out on top. For example, a tubby, slow, poor technique catcher with a cannon arm might beg the question of why isn't he a pitcher (because he ain't a catcher)? But in general, superior velocity gets a first, second, and maybe a third look.
So, an unpolished catcher with questionable technique but a very strong arm and clear athleticism will likely get the nod (for college recruiting purposes) over a highly polished catcher who does everything right defensively, but has an average arm. The presumption is that the blocking, framing, and running the game can be taught.
Of course, size, projection of added size, and hitting (especially for power) factor in immensely.