If you have a good specific https://en.wikipedia.org/wiki/Specific_impulse , and you can get decent https://en.wikipedia.org/wiki/Mass_ratio s in your lower stages, then 2 stages are definitely the way to go to LEO. Every stage over 2 adds a load of weight (more engines, structure, etc.), lots of ground system/support complexity, and a whole 'nother stage separation worth of failure modes.