[member="Hakora Feanor"]
I generally keep tabs on who's the best at writing the spirit of various combat styles with the character experience to back it up. I'm a little behind the times, but off the top of my head, my guess would be...
Form I: Shii-Cho - Ashin Varanin. I don't know any other senior Masters who have Shii-Cho as their exclusive primary style, and if there are, I can probably whup'em.
Form II: Makashi - My money's on Reverance.
Form III: Soresu - This one I don't know. There's an awful lot of Jedi Masters running around who claim blademaster status, and frankly I'm behind the times on telling'em apart combat-wise. If Ben Watts was around, he'd have my vote.
Form IV: Ataru - Soliael's writer has a definite flair for that kind of acrobatic, flamboyant combat, and plenty of competence in it, though I'm not sure if any of his current top-tier characters focus on Ataru. The other name that comes to mind is Raziel.
Form V: Shien/Djem So - Kaine/Vornskr and Cavill/Kryptus come to mind, but for my money, the absolute best Djem So fighter on the board is Alen Na'Varro.
Form VI: Niman - Not a clue. I can't think of any high-level Masters that have Niman as a primary style and enough lightsabre focus to be serious contenders, though I'm sure there's one or two floating around nowadays.
Form VII: Juyo or Vaapad - Darron Wraith, hands down, full stop.