Personally, I hate rumble because of how huge his impact on games can be.
The little turd can be incredibly disruptive, building durability, Rylai's, and spamming his shield while he mucks about in the frontline and does considerable damage. One would think that this much durability would mean that he can't output much damage, but, for some unknowable reason, Riot gave him an absurdly powerful ultimate with very high base damage, long range, a huge slow, and a fairly short cooldown. This one ability has won more games than should be possible. I well placed (and I use the term loosely because it's so huge and has such a short window to dodge that I hate to assign skill to it) Rumble ult can completely ruin an otherwise even fight and is very frustrating to play against.
It's not that Rumble always wins necessarily, just that he has such a huge impact on the game, and if everyone doesn't focus specifically on countering him he will run away with the game.