I think the question becomes what size, shape and part of the rig are you working on and what is your time frame?
Molasses( farm supply house wet or dry type) only takes a week or two of soaking for most serious rust and gets inside of area's reverse electrolysis misses. ( I have a toy gun that was buried and came out of the ground almost unrecognizable that has been soaking for 6 weeks and is now almost completely free of 'crud')
RE only takes a few hrs to a couple days but needs maintenance to work properly on badly rusted pieces.
Ospho (available at marine supply houses) does the job in hours to overnight... requires some extra work if your using certain epoxy primers, but for some pieces it's way easier and quicker than the RE or Moles...
Molasses is the cheapest route IMO
Ospho the easiest and quickest.. again, IMO, YMMV
