My reactionary thought is Eric Decker. Not only is the guy big, but he's fast, and seemingly has good hands from what he's shown. Even better, he's his team's unquestioned #1 target in the short term; Lloyd is out and will deal with a nagging groin for at least another couple weeks, and Eddie Royal (who's never had chemistry with Orton anyway) went down this week.
When you look at how good his performance was (5 catches, 113 yards, 2 TDs), as well as how useless his fellow receivers were (10 catches, 82 yards, 0 TD spread out among six guys), Decker just might be legit, ala Miles Austin a few years ago.
Lafell is relaly starting to come on strong. He's made some nice catches and was a very under the radar WR this year. I'd snag him up. He's showing great chemistry with Newton and they will need another WR to step up to help Smith/Olsen/Shock.
I would lean lafell slightly over decker. They are both basically the same size, but I feel like lafell will have more opportunity with a secure qb situation. If the broncos start losing, and brady or tebow come in, I would be down on decker.