Best mid lane mage?

I think its invoker he is very versatile. and maybe viper

st 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 champ

Lux, Leblanc, Ryze and Swain are the best mid lane champion. They are hard to counter specially Lux.

well you should try some out and see what suits you the best.