Call me crazy, but PS5 will take it.
Switch will do crazy well, but will probably drop at least a few million units from this year. There might even be a drop of 5 million or more. PS5 had the biggest console launch ever. Now that doesn't mean everything for momentum or lifetime sales, but it's something.
PS5 also has some key cross-gen, console exclusive, multiplats, and true exclusive games out next year. God of War V, Ratchet and Clank, Gran Turismo 7, Hogwarts Legacy (I foresee this one selling very well), Horizon Forbidden West, etc.
This is a more out there prediction. It's probably more likely that Switch will sell the most, and PS5 will place second. If Sony can't meet demand, that's even more the case.
Call it spite, being a contrarian, or whatever. But my bet is on the PS5.
I expect the PS5 to sell very well, but I don't see it selling 20 million+ in it's first calendar year.