You know, I've never really seen a magic system that I felt was completely right. I've always felt I was "settling."
It's been a long time since I used the Dragonquest system. I'm not even sure I used it when we played DQ (can't remember what type of character I was playing). I did, however, use the magic system in a couple of Melanda, Land of Mystery campaigns. I felt it was a good system to graft onto other systems.
The Sovereign Stone system seemed like an interesting variation for a low magic world, but I never got to test it. It did feel like the spells should be a bit more for the length of time required to cast them, though.
For D&D, though, my favorite is Monte's Arcana Unearthed/Evolved system. Heightened/diminished spells are something I absolutely would like to see in the next update of the D&D system. Spell templates are a nice idea, allowing variations on spells without having 6 variations of the same spell floating around the books. The only thing I'd consider changing is keeping the divide between divine & arcane magic in some way.