Polishes are a personal thing, like oil. Everybody has their preferences.
Nothing beats buffing aluminum parts with cotton wheels and stick compounds. But there's an art to it. And you have to remove the parts first to do it right. I use a white compound followed by pink (ultra fine). For hand polishing there's Mothers, Semichrome, Autosol, and a host of others. Take your pick.
For major non-polished castings (crankcase, head and gearbox), Simple Green with a Scotch scuff pad works extremely well. Chosing a cleaner depends on what you're starting with, how far you want to go and what your intentions are.