There are no "best" or "worst" heroes, The champions are only as good as the person playing them is.
AND if somehow you managed to "balance" all of those skills, now you get to the hard part of throwing in the permutations of them being on specific team combinations and actually working in conjuction with one another. not gonna do the math for you but you're looking at something like 3600^17 different possible ways the game could be played out.
yeah, good luck trying to balance that and tell us that there are no such thing as tiers.
the best you can do is just to keep patching the game whenever overwhelming/underwhelming strategies present themselves and just keep getting closer to truly balancing your game, something that I think riot is truly trying hard to do, so props on that.
but back on topic:
Top 3 most Powerful (I'm assuming you meant straight up killing power):
Top 3 Usefull (Assuming this means Top 3 highest placed on tier list):
Worst 3 (3 Lowest on tier list)
-Jax or Warwick
Just my 2 cents. xD