League of Legends (LoL) Question: What jungle should i buy?

Gragas, Rek'Sai, Vi are all decent.

Dr. Mundo is a very tanky jungler. His passive Goes Where He Pleases is a useful sustain tool in the jungle. Once you hit level 6, Maximum Dosage gives you pretty much infinite sustain. cinderhulk is an excellent item for Mundo, because he does not need to build damage items (but they are fun if you are super fed).

As said, Vi and Rek'Sai are good choices. Volibear is great too if you don't mind going full tank (you still deal good damage with Frenzy 's execute).

If what you want is tanky+lots of damage you may want to try one of the newly buffed champions that run Enchantment: Devourer. Vi, attsp Fizz, Jax, Udyr, Shyvana and Warwick are built tanky and deal good damage once they charge the devourer. Xin Zhao, Aatrox, Rengar, Kayle are a bit less tanky but might be what you're looking for too.

I would recommend Wukong, a bit similar to Shaco due to stealth, tanky bruiser with a lot of burst dmg.
Also Shyvana can work, tanky and deals a lot of dmg with new sated devourer - kinda more tf oriented Nocturne.

Both are tanky and both have nc dmg, great for soloq.

Trundle. hes a bit squishy early but pretty tanky mid-late still does a lot of damage

Rek'Sai is a great choice if you want a tanky but damage dealing champ.

I recommend also trying out Ekko and Teemo jungle as well.