It'd be a tossup between RL 15 and Varget. There darn near clones of eachother. The only problem is I've worked up great loads in some guns with one powder, and great loads in other guns with the other.

I've used them from 308 to 500 Jeffrey, and a few in between, also in some contender chamberings.

H 4350 is also a good un, but just a tad too slow for the medium and bigger bores.