I agree with Vyn, unless you don't care what you enjoy and only want to win. In that case, perhaps try Viktor or Azir for general purpose mids. Or if you wanna show off and look cool, Yasuo or Zed.
I strongly disagree with the sentiment of "unless you don't care what you enjoy and only want to win".
You'll be most successful playing whatever champion/role you enjoy, because it enables you to really master that champion instead of getting bored after 2 weeks of playing a champion you like. Even if it's something unconventional, it's easy to get Diamond as long as you're good at that thing.
I got master without playing the top-tier supports at that point in time - I just greatly enjoyed those champs I did play and that allowed me to really master them (pun intended)
I've always found ahri to be my go-to mid laner, she has little counters, is useful when behind, and can carry games when fed or well farmed. All you need to master is her ult and charm, because your w is a lock on ablity, and your q is just follow up from landing your E. Her downsides are that she really needs to land charm for her kit work fluently, her ult is not normally used for damage, it should mostly be used for utility, and her items. Now you need to be good at farming while playing ahri because you scale with items, and the items you need are expensive, and you can't just spam q on the minions because your mana pool is pretty small, so make sure you have Arcane Blade in your masteries to help with your last hits. Her early game can be pretty good if you use it right, ever since 5.9 she is no longer considered an assasin, shes a control mage with a great mid-late game. Keep that in mind every time you ult for a fight, you don't have the highest amount of damage compared to other mid laners, but you do have insane mobillity and cath potential and the threat of charm keeping the enemy team back.
You'll be most successful playing whatever champion/role you enjoy, because it enables you to really master that champion instead of getting bored after 2 weeks of playing a champion you like. Even if it's something unconventional, it's easy to get Diamond as long as you're good at that thing.
I got master without playing the top-tier supports at that point in time - I just greatly enjoyed those champs I did play and that allowed me to really master them (pun intended)
I jungled AP Leona in inhouse games twice and I had fun