Rumble isnt that hard, he is a cooldown based champion so no mana, full ap based so you build the tanky ap items and his max shield can be massive, good wave clear, ranged harass with slow on his harpoon. the only hard part of rumble is learning how to properly use his ult, because you have to draw a line where you want it to go, and managing his heat bar. Shen is decent top, but he actually takes some practice. he is low damage and solo kills require champion mastery. Rammus is a very good jungler, and can get to where the ganks need to be happenin VERY fast with his power ball...plus tanks are in right now and he is a good one.
For top id pick rumble out of the ones you have listed...however my personal favorite is 