Best mid lane mage?

I'll just give you an overview of the champions depending upon the division first:

Platinum+ Aurilion Sol
Platinum Zed
Gold+/- Zilean

However, you don't have to start mastering the champion which is listed above just because they're OP for now. Go for the champs you're comfortable and have sustainability.

I'll enlist the champions which in my opinion, may help you in lane:

Ahri (good escape plus burst late)
Lux (long ranged spells, CC and OS)
Annie (easy farming even if you're behind and can turn the tables late game with flash+ult combo)
Zoe (heavy burst and OS but difficult to master)

Hope you can do well, good luck!