Hi there, I'm Bat and I almost never play Summoner Rift, because I find ARAM more fun.
95% of my games are ARAM, so I've seen pretty much and believe that have a good but unwritten statistic of what champs are better than others.
VERY IMPORTANT NOTE
Disclaimer: this is completely based on my opinion of the best champs in ARAM.
I firmly believe that any champion can be good of played correctly.
These champions can all be good in the right setting, so always check your team composition.
And I'm sorry if there are mistakes in grammar, English is not my first language :)
There will be updates and more comments some time soon.