it may depend more on your point and roster settings. Any of Jennings, Moss, and Floyd could have a big week, though it's not likely that all do on the same week, plus you may have a week like last week. But at least there are three of them, so you have a few chances.
With a QB, you only get one shot. And in the 2 leagues I'm in, getting solid numbers from your QB is a must. With Rodgers, they have no real RB threat, so he's going to get his yards and TDs. I just think I'd rather take my chances at WR, knowing I haveRodgers at QB. Plus Moss going to the Vikings could be huge.
I've had Garrard before, and he's pretty inconsistent. This year, his TDs by game are 3,0,1,2. I think he's just what you said - a backup.