I'd hate to limit myself to three stones! Still, you can do a good job with just three. As for which ones, that depends on what you're sharpening. I personally think the Naniwa Chocera stones are the best synthetic stones out there (that I am aware of) but they're not what I'd recommend for sharpening a bunch of "super steel" stuff (eg M390, HAP40). Shapton GlassStones will cut just about anything and everything there is but they're not as nice to use as the Choceras.