-
No champ in this game can 1v5 a group of skilled player on their own, however I think what you are looking for is a champion that can split-push and single-handedly either kill or get away from 1-3 players on the enemy team at a time. These champions come to mind:

-
Not braindead easy? Of those I mentioned above, I would say Trundle and Udyr are the easiest, but "easy to learn" and "hard to master" are different things.
-
All the champions I mentioned can play top or jungle, and can take damage and well as deal it very effectively. Some can even mid.
-
That is opinion based, however I do think that Demonblade Tryndamere is the coolest damn looking character in the game. Renekton also looks cool as hell.
-
A lot of the champions I mentioned have very aggressive playstyles. However, if they are not what you are looking for, I would like to introduce you to the #1 assassin in the game: Talon
He is hyper aggressive and snowballs like a boss.
-
All of the champions I mentioned, with the exception of Talon, are hard to kill and can handle themselves. They all have much in common and I strongly believe over time you should learn each one.
All in all, I feel like Tryndamere would be your favorite champion. He is only 1350, and I've seen good Tryndamere's completely dominate games. Here is an example of that, definitely watch this if Tryndamere is someone you may consider. It is of a player hardcore carrying his team through a silver game.
https://www.youtube.com/watch?v=LVd7mMU1Yck
If not, do you want a champion that is very strong early, falls off late game?
Or a champion that is weak early, but strong late game?