I'm going horde so i'm also looking for input between druid and war tank.

I did some of my homework. I can say that those 2 are viable for 5 men. You get a stat buff with a druid tank.

Druid tank can cast regrowth and rejuv before pulling and have thorn (plus fire shield if you have a warlock). That give a bit of aoe threat. If you get more than 3 mob it help to keep agro over your healer at start. you got swipe that damage 3 target, this is easier to make threat but can break cc. If i'm not wrong druid do less aoe threat than warrior but more single target threat. With a warrior you will have to switch target to make aoe threat with revenge and sunder armor. You also have battle shoot when you have pull that make a good aoe threat.

Druid take more damage than warrior but have more hp. Because druid take more crit and crush than warrior. They have more armor but that dont compensate.

Druiid add a rez battle and can off heal if needed. That can be usefull for pvp or some fight for pve.

Overall I think warrior is a bit more difficult to manage than a druid. A warrior is better if you want survability and a druid is better if you want something easier but full of utilities.