[Brownell's rust bluing is] all I've used on any of my projects, so I can't make any comparisons to other products, but it is the least expensive I could find (not counting the homemade recipes you can find on the web), and it made the parts rust every time
I have heard good things about Loural Mountain Forge's Gun Browning and Degreaser
. As it is a degreaser, it is (supposedly) more forgiving of oil contamination. Anyway, I plan on using it, but won't start until I finish up refinishing the wood on a marlin 39m (a couple days now). Even then, I will be polishing the rust out of the old Iver Johnson.
And, since my eyes are always bigger than my stomach, I just bought a Colt 1903 for a follow up project.