If I’m understanding correctly, you’re asking about levelling through questing as a tanking class?
Any of the tank classes is more than capable of pulling as many packs of mobs in the world as they can find. Tanks are built for pulling packs of elites in dungeons; packs of non-elites don’t present a problem. Even Warrior tank gets decent heals through Victory Rush, where you can get 20% of your HP back when you kill a mob. If you’re pulling packs, and nobody else is there to steal the killing blows, you will get plenty of heals. The problem for Warriors comes mostly from tackling big, single-target elites where that heal is not available.
Still, Warrior and Monk are the two tanks I don’t think of as ideal for soloing.
In terme of my personal preferences:
My personal favourite for this kind of thing is Paladin. Decent damage, very controllable heals, lots of utility.
Druid would be great because it can do all roles, and Boomkin can be extremely handy for farming, but I find Bear dull to play, and turning into animals doesn’t do much for me.
Blood DK does have the craziest self-heals, but it is also the slowest.
If I tried to play Vengeance in the world, I’d switch back to Havoc too fast.
But really, of those 4, all are more than capable. You just have to find out which you like the look of. If you have a Class Trial, that would be a worthy experiment, or look up videos on Youtube. Or they all have their basic class toolkit by level 20, so you could try them until level 20 and switch if you aren’t satisfied.