Tennant/10. He can at very least confuse/excite them with his constant blah blah blah-ing. Also he'd be most able to tell if they are a threat or not.
Also seeing David Tennant greet Aliens would totally make my day/month/year. He'd be all like "but I'm only an actor" and we'd be like "yes but you're a very good actor and you make funny faces, get going".