Rangers are, without a doubt, the best pullers - you're less likely to be aggro'd, you can spot more enemies more easily, and you've got the bow for grabbing their attention. Also, because you're a ranger, you can do more damage with your archery skill than others, so the mob is already hurt before getting back to camp.
I'm thief, about to get Ranger. When I get to lvl 30, I'll have the high-powered range shots, so I'll be pulling. Run back to camp, get the WARs to grab the aggro, then pop in with a few ranged shots until TP is high enough to SA/Fast Blade.
Talk about a damage-dealer.
Thief also works well with gilfinder and treasure hunter, so you can pay for all those arrows you're using.
On the technical side, both thieves and rangers base their attacks on their AGI and DEX, and both have advantages in both; using the two together makes both better. From what I've read, it seems to be one of the more "natural" matches in the game. There aren't many now, but most US players are JUST getting to lvl 30 and the advanced jobs, so you may start seeing more.
"There's a new twist in the game."