Do not worry about the coming changes, play the class you enjoy. Just looking at tanks as the best it would be the Guardian, the Captain, the Beorning, then Champion or Warden. Unless, you are talking specific instances, then there is no real order for the best tank.
The Guardian, Captain, and Beorning are single target tanks with some AoE. On the other hand, the Champion and Warden are AoE tanks with a little single target. Between the Champion and the Warden, though both are AoE, they operate in very different methods. A Champion can shing-shing all day, until their stuff is on cool down, then it gets dicey. A Warden is an AoE tank, that now needs assistance in healing, if tanking, with few ways to instantly grab agro, and they do better with 6, 8 to 10 mobs at once. However, interrupts and most Bosses are deadly to a Warden. Wardens are medium armour.
My two coppers...
Ujest - 140 Lore-master, Opun Tia – 107 Warden, Tummi - 105 Captain, Veneur - 75 Hunter, Cneasai - 66 Minstrel, plus alts and mules
Officer, Pipeweed and Ale, Arkenstone (formerly – Friends of Frodo, Vilya)
and Star Citizen…