I don't think there is a best, just different. Thinner seems to smoke more and dry out faster and too thick cools some elements too much to smoke.
E.g., Add thicker Protosmoke to my post war and they are mostly happy. But use it on the fluid Generals and you might need to. wait a few days before they smoke again. On the oppsing side he 3 drop resevoir means thinner fluid vanishes quickly. It does best mith a medium viscosity; old 1960s-70s tubes work best. (I dont.have the Lionel Premium)
I found a grape scent I like from Pat's/P&P's that I've used.for years now just because I like it.'s smell.
I've been mixing them for many years and all I've seen worth noting is on pellet type, fluid on wicked pill residue makes a goop that doesn't seem to flow or melt, it just gums up the wicking.
