I brought up Sioux City Sarsaparilla in an earlier post. That's the best I've ever had.
If you can find it try their birch beer as well. It is a like a light cream soda. Not so much vanilla and a refreshing spice note. There are a few others Sioux City makes that are along the same vein. The best, they quit selling it locally though. Grocery store change.
I'll quip in with Oscar as well and say have you had a chance to try it yet? Would be interesting to hear someone's take on Root Beer that hasn't tried it.