What are the best magical systems in GURPS?

[Blind Mapmaker]

If you know what you're doing, it can be fun to mix and match systems, especially if you have a kitchen-sink fantasy setting with wildly varying traditions. In my current campaign, I'm using modded Standard Magic for the majority of nature-based casters (further modified by tradition), heavily "stylised" Standard Magic for the academic mages with grades dictating what you can learn when, modded Path/Book Magic for shamans, Ritual Path Magic for geomancers, Sorcery for magic fools, Magic as Powers for untrained casters and Divine Favour for clerics.

It all depends on how different you want them to be and how much time and effort you're willing to invest. Oh, and you probably don't want to do that if you're cursed with munchkinny players that are just waiting to exploit the smallest inconsistency.