Wonder if we're just talking about the PS5 and Switch SKUs.

Probably Mario Wonder.

It's wonder

I think people are confused with Spider lifetime sales, mixing Mile Morales together even though they are different games

Spider might surpass wonder with a PC release, but the inevitable Switch 2 Deluxe version will put Wonder at lead again

For clarification, I meant the Switch release of Wonder and the PS5 release of Spiderman.
Potential future releases of Wonder for Switch 2 or Spiderman for PC not included.

Super Mario Bros Wonder by a lot.

Super Mario Wonder by a lot, especially considering the install base and that Super Mario is way more popular. The sales of Spiderman Miles Morales are lower than the original. I doubt the sequel is going to debunk that trend

I could see Mario Wonder hitting 20 million and Spiderman 2 hitting 10 million plus sales. When it's all said and done, it's possible Spiderman 2 ends up with more players when it eventually comes to Playstation + essential in a year or so.

Super Mario Wonder will sell more than Spiderman 2 on PS5.

Spiderman 1 and Miles Morales on PS4, PS5, and PC managed to sell 33M units. The split is something like 65/35 last checked, if that ratio remained then Spiderman 1 sold around 20-23M units, and possibly a little more since the data is old (but I wouldn't guess much more).

New Super Mario Bros U Deluxe sold 16M on the Switch alone, and that game is just a port of a game already on Wii U (not to mention it didn't have the hype of the recently released Mario movie behind it). Mario Odyssey sold 26M units.

So, yeah Mario Wonder for sure.

Wonder will sell more in the first year or so, but since it's on a system that'll soon be replaced Spider-Man 2 will start catching up after that, the first game basicly had legs like a Nintendo evergreen after all. It could still go either way though, I don't think Wonder will sell as much as the first Spider-Man (including the remaster) but I'm also not certain its sequel will either unless it's very well recieved and gets people talking for a long time, but if I have to guess I'll say Spider-Man 2.

If we're not counting Switch 2 sales, then this will be determined by when the Switch successor launches. If it launches in 2024, then the switch only legs for wonder will be cut off early.