I say Invite-only, and if they ask, then say "Play a match or two so I can see how you play".

I am getting pretty tired of newbie players who are not active, contribute nothing to the clan, and who suck at the game. Invite-only ensures that only good and active players are added, and those players are exactly who we need. Why not? Do you people not want good and active players? Of course you want good players, invite-only then.