I'd take Saquon Barkley at #1. You'll still get a good QB at 4. There is no consensus #1 QB in this draft. All the Josh Allen hype doesn't change the fact that he's a project - the kind of which could ruin a GM. There's no telling which of the top 4 QBs will be a star. Allen is the least safe of these.
Let's say that the Browns GM takes Rosen or Mayfield at 4 who goes on to have a career like Alex Smith or Phillip Rivers. That won't kill your career but whiffing on Allen at 1 would.
You can't screw around with the #1 pick overall. It has to be a safe bet. Coming out with a HOF RB and a solid, occasional Pro Bowl QB is a very good draft.