Best Middle ?

Every champion is good in it's own way.
To play and level i would say low tier midlaners like: Veigar and Annie.
To learn how to play and be good at the game at a point where u can reach platinium or diamond... I would say LeBlanc, Talon, Fizz, Ekko, Zed... What do they all have in common? Roaming potential. You roam bot, get a couple of kills and snowball and get your team ahead, and late game they can destroy the adc's in a teamfight, even if you die, you take out a major player in their team. Their constant source of damage.