I'm a relatively new paladin to WR, but I played one for years on Live. So what I'm about to describe is based not on WR experiences, but on EQL. That said, it's my belief that stuns are the spells of choice to generate aggro. I have seen some people use Flash of Light mixed in with a couple of stuns, but I never saw a benefit or need to do that. I just rotate Cease & Desist with a 3rd stun and I never have a shortage of aggro and I can chain-cast them until I'm OOM.
Root is actually a bad idea for aggro control. As was stated, rooted mobs will attack the closest PC to them, regardless of their hate list. This makes it difficult when multiple melees are in a group and you want to keep aggro on the tank. A rogue or ranger who get a little too close could become mush in a hearbeat. In short, root is good for ghetto crowd control when you don't have an enchanter (you run away from the group, root a mob, and run back so the rooted mob can't attack anyone) but that's basically it's sole purpose.