Look at the difference between Doctor Strange’s and Loki’s character hubs.

Thanos

. J. Jonah Jameson

. Peter Parker

. Loki

As far as who we’ve seen on screen? I think Loki

Everyone has the same amount of Variants, and some look exactly the same as their Variant in a other reality (like the Strange Variants we see in What If...? and MoM, President Loki and some others and Raimi J. Jonah Jameson). But in every universe there's a Variant of that person, but on screen I''ll go with Loki. Everyone we've seen in that group of President Loki in Episode 5 is a Loki I thought...Peter Parker had only 3 others on-screen (Peter 2, Peter 3 and Zombie Hunter)...

Everyone except of America who is unique and Billy with Tommy who died in WandaVision I think everyone has as many variants as the universes

Well in theory, everyone has an infinite amount of variants, but in movies and shows, I think Loki or Doctor Strange can have the candidate, but the award in amount goes to Loki, and the award in power goes to Doctor Strange, which Strange's variants have been shown to kill or destroy entire universes.

I would say Spider-Man: No Way Home did

I'm gonna have to say Loki.