Top lane

Rumble is more rewarding, Gnar is probably more fun.

depends. both champs bring totally different things to the table

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or TOP?

If you want a shredder go for Rumble. If you want a high CC based tank go Gnar. It all comes to current team comp needs.

both have pretty unique mechanics to get used to, and play very differently...and accomplish entirely different things. (Though both are amazing for teamfights)

With the upcoming changes to armor and other things, I actually foresee a lot of AD being on teams though (AD mids and jungles both are likely to be popular in yolo-queue ) So picking up Rumble might not be a bad thing to have a really good AP top laner.

Gnar is better at split pushing, and initiating a teamfight. Rumble is better at teamfighting in general, but generally as cleanup and backline damage rather than a primary engage. And his split push is rather weak.

So if you already have decent AP tops ( ) then go for Gnar. If not then I would say add rumble to your pool P: