#21, hands down.
I detailed my 2014 Altima last October using a PC 7424XP DA orbital buffer. I used Pinnacle's Advanced Finishing Polish before using the M-21.
Both the final result and durability were great. It was still beading nicely and looked good when I detailed it again in late May.
According to a couple of professional detailing shops in this area, Meguiar improved their formulation of #21 earlier this year. In what way I'm uncertain but I like that product and will continue to use it.
Your mileage may vary depending upon several variables, including prep work and how you choose to apply it, i.e., by hand or DA.