I think it would be Jeff as he did literally go to an art school while none of the others did.
Also the Legion asked him to spray for them so it is very likely that they aren't very talented at it.
Nea also does graffiti but not to sell it or to make it look good just to rebel against the government/parents
Nea, since that's her thing.
Jeff is likely the best artist, but that doesn't mean he's good with spraypaint.
Nea would probably be the best using that medium.
Legion is just a gang of teens that get in trouble that goes too far, they probably don't have any actual skill.
Jeff is an artist- his perk descriptions are written in what canvas size he used, and what type of paint he used. He spray painted when he was in Highschool, but if they were to have a graffiti off, Nea would likely win. However, if it were a paint off, Jeff would win. He may have drawn; but his perks mostly say that he used oil.