Gavin is an SF Democrat like Kamala Harris (currently a coin flip).I don't think she's a realistic national candidate. At least not in the context of who she'll have to go up against in any future primaries (Mayor Pete, Gavin, Moore, etc).
I'd take my chances with Big Gretch, because of the Rust Belt. I said this before Joe Biden dropped out, but unfortunately I don't think I'm wrong so far. Obviously I hope I'm wrong when the voters in 7 battleground states cast their ballots. (So far, Harris has run a solid campaign so I can't complain about that.)
Of course Newsom is a white male, with an actress of a wife, so I wouldn't say he's completely unelectable. But he's the face of California these days, and that carries a lot of baggage for certain people.