It depends on what kind of gun you want, for a French Fusil with a straight stock I would go with RE Davis for the Fusil de Chase from Tulle I would go with the TOW 44" barrel parts set and give the lock a work over cosmeticaly, for a NW gun or Early English I would go with North Starr West, for a fowler I would go with Chambers. I think these are the best bets for the various type of guns, I have no experience with Sitting Fox, TVM, Petaconica or the others but from what I have seen on their sites the HC/PC factor on some guns, mainly French is sadly lacking, The sites I mentioned are about as "correct" for the type of gun as you will find short of ordering parts from the Riffle Shoppe and having a premier builder do the work, following originals as a pattern.Just my opinion based on many post on these forums and personal research and using parts/putting together guns from some of the vendors I mentioned.
I always consider the PC/HC factor as part of the "quality" factor of a ML kit/gun. I think they are inseperable considering that the object is to work towards a "replica" of the originals, not to say that guns that fall short of the level of "correctness" that is possible are bad, just that they are on a different level when compared to a well researched gun that strives to follow the originals as much as is practical.