What are the best magical systems in GURPS?

[AlexanderHowl]

Of course, as the Temporary Enhancements and Using Abilities at a Default rules are generally need for Magic as Powers to work. Of course, designing a set of abilities can be an annoying amount of work, but that is the utility of having leveled traits. For example, you could have a magical system with ten foci, ten abilities per focus, and ten levels per ability, allowing for one thousand steps of potential advancement.