Unless things go horribly wrong, Arch Manning is probably going to be the first overall pick. He's the current favorite, according to FOX Sports, at +225. And if he doesn't, then there are some other QBs who could take that spot, like Cade Klubnik, Drew Allar (who is not far back at +275), and Garrett Nussmeier.
What if it's none of those players? What if it's not even an offensive player? That would be a big shock, especially if it ends up being Caleb Downs, the defensive player with the highest odds of going first overall, though he's still a long shot at +2500. He's behind those aforementioned QBs and LaNorris Sellers, and Sam Leavitt.
Downs is tied at +2500 with T.J. Parker, but his candidacy makes more sense. Edge rusher is much more valuable than safety. It's arguably the second-most important position in football behind QB, so his being up there makes sense. Downs shouldn't be. There have been no safeties taken first overall since 1991.
Downs has an outside shot at it, though he has his work cut out for him. He is PFF's second-best collegiate player behind teammate Jeremiah Smith, who is notably ineligible for the draft. How can Downs climb the leaderboard over all these good QBs? It would take a perfect storm.
First, some of these QBs would have to have down years, and others would need to opt to stay in college. This is what happened last year, as several projected first-round picks didn't even go pro. Second, the team picking at the top would need to already have a QB, so it would need to be some team whose quarterback got injured. It's a tall task, but the Ohio State safety has a shot at it.