Best 4 Stars to Level Up?

Hello, first post here and I was wondering which 4 stars are the best to level up. I currently have way too many 4 stars than I know what to do with so if I happen to have some of the stronger ones I'll start leveling those and sell the rest. If you'd like me to put together a list of all my 4 stars I'd be happy to do that as well. There are just a lot of them so I don't want to waste time typing a list if it's unnecessary. Thanks!

if you look on http://www.fantasicawiki.com/wiki/Help you can compare stats/skills/event arena skills, with that info you can find out what you want to lvl up first.

Usually focus on leveling 10 cost 4*s that have a decent speed and skill like Zafriro C speed slow and Nanael B speed knockback, they come in useful as fillers when u dont have stuff like charles.