Roger Delgado. The original and best. As I've mentioned elsewhere, the way he, Jon Pertwee and Katy Manning played off each other greatly added to the appeal of the Master's appearances.
Jacobi was pretty good, but then again he's a marvelous actor and always eminently watchable. Ainley had his moments, mostly when he wasn't hamming it up. I didn't find Pratt and Beevers particularly interesting and the little I remember of Roberts in the role is...err...not good. And I dislike Simms' ludicrously over-the-top Master every bit as much as I dislike Tennant's Doctor.