I have tried about a dozen...Which isn't that many these days, seems everybody is making cables. Best that I've heard with Maggie's is Cardas Golden Reference (especially with a nice sounding SS amp like the Plinius).
The so-called "best" is very subjective and depends on component synergy, room, etc. I am using the Analysis Plus Oval 8 speaker cables with excellent results with my MG 3.5. In my system these cables provide the high current delivery required by maggies. These cables allow my system to be transparent, coherent with a "full" midrange balance and a huge soundstage. Treble is also extended and sweet with powerful bass. I have experimented with some mega$$$ cables, and I find that the Analysis Plus Oval 8 provides a level of performance comparable to the Transparent Ref with XL (with better top end to boot) and some other very expensive cables.