It depends on what you want for a magic system.
I tend to have a favor Ars Magica's Verbs and Domains, while simplifying it, because i'm not willing to play researchers in magic fields.
WoD's Mage is cool too, but I won't call it simple, it asks for a lot of abstraction.
In Fate, especially in the toolkit, there are a few magic system described , and they're good too, one of them is a declination of Ars Magica's by the way.
A game in french has a very good system too. "La Brigade Chimérique". It's more designed to run superpowers, but depending on what you want to do with your magic, it does wonder. I used that system before, and it is as simple as efficient.
Finally, if you want to test something turnkey, i would suggest you have a look at Maze Rats.
Last edited October 15, 2020 10:03 am, a total of 2 times