#however these have been hyperfocuses of mine for 22 years now

[eevylynn]

The answer would honestly depend on a lot of different variables.

What are we talking here: 1v1, 2v1, 3v1

Would they all be at school aged or at the point that each died?

What kind of fight are we talking about here? Friendly sparring? Duel to the death? Muggle fighting? Do they all hate each other in this scenario? Are they all friends still? Or is this like afterlife schenanigans?

Are we strictly going by canon personalities and skillsets? Or is this some non-canon fanon verse where their personalities aren't quite in line with the books?

While James surely has the skill, he doesn't have much in the way of bloodlust when it comes to his friends, even if they did end up on the other side of the war. He would definitely hold back. He's also a tad overconfident in his abilities and lacks "constant vigilance"

Sirius has reasonable skill and a helluva lot of swagger to back it up. It's probably why so many people are voting for him, to be honest. He definitely has enough bloodlust to do it, EXCEPT when it would come to fighting James. Also, Sirius honestly doesn't have a good canon track record when it comes to dueling. He lost to Peter Pettigrew. Yeah, he was grieving, but still...

Remus's skillset is honestly probably about the same as James and Sirius, he's just less showy about it and more willing to talk his way out of the situation before lifting a wand. At most, he's slightly less powerful than James and Sirius. He's also insanely fast at the draw once he's willing to fight. (I'd probably put him and James at about the same in speed, given James' chaser reflexes) What really gives Remus an edge over the above two, though, would be his utter ruthlessness. I don't know if it's his werewolf side, but once Remus has written you off, that's it. Good bye.

Peter. *sigh* Technically, he beat all three at one point or another. (In a backhanded way, but beaten nonetheless) That being said, whether or not he would win in a 1v1 fight with the James and Remus would 100% depend on the situation at hand. (He canonically beat Sirius. That is not a question) Peter is NOT as skilled at dueling as the other 3. However, he's just as much a Slytherin as he is a Gryffindor, and he'll use what he can to win. He is not afraid to use underhanded techniques to ensure his survival, no matter who he's going up against.