I would go 1) T.J. Yates; 2) Shaun Hill; and 3) Charlie Batch. I'd lay money on any back-up Eagles QB not named Vince Young.
Campbell and Orton are only back-ups by circumstance. Orton hasn't been a back-up since his early days as a Bear, and Campbell's never been one yet. They're just failed starters.
What, no love for John Skelton, or is he considered a mediocre starter? Since he's "backing up" Kevin Kolb, it's probably the latter, sooner or later.
It feels weird to call Locker or Kaepernick "back-ups" because the plan is clearly to go them when they're ready.
Question: Who's the better historical back-up quarterback, Jeff Hostetler or Earl Morrall?