Z'zgashi
Smash Legend
Just play whoever you like/are good with. Every champ is good enough to be viable in at least one position and there's no true, clear cut best since the patches make the game change so often. Your best bet is to find a handful of characters you like to play in each position, get good with at least 2-3 per role, and stick with them while finding which role you most prefer. Once you find your favorite role, try and concentrate mostly on that, but make sure to still have pockets for the other roles as well.
EDIT: The exception though is Fiora, she's the best.
Best Solo Q champs atm though I would say are probably Lee Sin, Nasus, Riven, Nidalee, Thresh, and Leona.
ANOTHER EDIT: Just checked my YouTube sub box almost right after posting this and found this in it which is somewhat relevant: https://www.youtube.com/watch?v=U9w3vRNvgu4
EDIT: The exception though is Fiora, she's the best.
Best Solo Q champs atm though I would say are probably Lee Sin, Nasus, Riven, Nidalee, Thresh, and Leona.
ANOTHER EDIT: Just checked my YouTube sub box almost right after posting this and found this in it which is somewhat relevant: https://www.youtube.com/watch?v=U9w3vRNvgu4