For me it's Kanati for one piece and Dryad Orion for three piece. I've never tried a two piece, so I have no preference there. Most of the custom bowyers will do their darnedest to give you a grip that fits you, but this question is like asking which girl is prettiest or which truck is best.
Everyone you ask will have his/her own opinion. My family tends to run toward wide palms and short fingers, so we can get along with pretty similar grips. For others, they wouldn't be worth a hoot.
Although I like the FEEL of Hill style grips, I can't seem to shoot very consistently with them. The Kanati and Orion grips kind of force my hand to be in the same position every time. Apparently I need that because I shoot them well on my bad days and great on my good days. I can't say that for the Hill grip. Your mileage WILL vary.