Remember Tanking is not about killing heroes or 1 man army. its about capable of going infront and take all the beating for your allys.

My votes goes to Treant Protector.

As he has does nasty base damage and have very high hp. his root armor pratically gives a free plate mail. providing him +10 armor thoughout the game.

If you have atleast 1 Heart Of taraque, if you are wounded you can just cast nature guise, hide 1 corner then get back to action.

2nd will be Pudge.

if you play your cards right, you can pratically have near godlike hp. You just have to be good with last kills.

if you gotten 2 Heart of taraque or a few ring of health, you can rot and heal in 1 go.

Abbandon is good also but Imo Abbadon feels more like a good escaper than a tanker. Cos Abbandon use his abiltiy to escape GB than actually get into battle.

Last goes to Centaur. Lvl 3 ulit = free reaver. get a plate mail and dagger. you are ready to jump into the fray.

The art of tanking is simple.. guts, You must be willing to jump into the battle and bite the bullet. Cos whe you time it wrongly your team will fail.

I dont find Axe a really good tanker. He has alot of limitation. I think he lack the HP.

Overall Axe imo feels more to an anti agi and an anti intel hero. since they dont have alot of hp so axe can strike them with ulit with just a few roars.