Seriously, this is a pretty obvious answer. The #1 "Solo Top Lane" champion is Rumble. He doesn't use mana, heat instead which pretty much comes in your favor. His Flamespitter can do major damage and push two enemy champions easily, as long as they're in front of you. Scrap Shield is great for escaping (unless you're fighting against Yi or Xin Zhao, who will chase you easily anyway). Electro Harpoon does not deal out the highest damage, but it has an epic slow, and if you hit a single champion with both shots, they won't escape your Flamespitter, and if they try, just dash with Scrap Shield. His ultimate, The Equalizer, is epic. Even after the nerf, just drag and drop a hazardous line of rockets doing DoT. As a finisher, slow them with Electro Harpoon and use Flamespitter to keep them running on the rockets until they die. If a low health champion is hiding behind a turret, drop it just in front of them, leaving a rocket trail behind them, slaying them easily.
After nerf Rumble is not OP, but if played well, he's still a gamechanger. Totally worth those 4800 IP.