Fisher,Heilman,Martini/Hagn,Gatti,Echols,and others,this is not a order of priority list. All have something great to offer.
Martini/ Hagn definitely have the best takedowns I have seen,threads are square form,tight,smooth,precise,chromed,no wobble. Great integral barrel feature work as well.
H&H would not get my money,unlikely I would ever buy one,considering what work is avail from these other great individual craftsmen.
Rhiemer Johannsen I was not over the moon about, But Hartmann Weiss do some fine work, However you could get their premium 98 action,sent to one of the guys above, get a damn fine job, and save $000s' over what H&W would charge.