I have a rifle that is finished in both Duracoat and Molyresin. The fiberglass stock is duracoated, the barreled action and all metal is moly resin. Both are tough finishes. The gun has been hunted hard for three years and still looks like new. The duracoat does create a thicker coating as you mentioned. This can cause fitting issues between tight tolerance parts. That is not a problem with proper application. I t just means you can simply give the whole gun a bath, cure it and let it go. You have to be more careful in your execution. Because duracoat forms a thicker layer I feel it is also more likely to chip.
Moly resin is applied much much thinner. It's thin enough that it can be used to coat tight fitting mating parts with out causing tolerance issues in most cases. For example, the entire reciever and bolt lugs on my rifle were coated with it with no isses with headspace. I think you can even coat threads on threaded parts and they will still screw together. Molyresin is also supposed to help reduce friction. It' doesn't really chip or peel, but can be worn through on high friction areas. In my case, the bolt lugs and high friction areas on the bolt body are starting to get some wear, but that's it.
In short, if it were me, I would go with the moly resin. Another one worth considering is ceracoat. From what I hear it is extraordinarily tough. It too is a slightly thicker coating though, and from what I understand a little trickier to apply.
Adrock1