Hmm- it's tough. I'm of the opinion that Matt Ryan is going to have a breakout year. With Julio Jones in the fold, and basing things off of the amount of passing the Falcons did in the preseason, and Michael Turner aging, it looks as if they are going to be relying more heavily on the passing game. I wouldn't be surprised if Ryan put up better numbers than Shaub, and finishes in the top 5 QBs.
However, I also think Stafford will have a breakout year too, if he stays healthy. That's the key question though.
On my team, I have both guys. Matt Ryan is my starter, with Stafford @ backup.
Personally, I wouldn't do the trade. Stick with Stafford as your backup, and keep Mike Wallace. Mike Wallace is the key point- no need to trade for guys that will just be put on the bench, when Wallace is a big part of your team. Ryan may be the better QB, but I think Ryan and Stafford will both have breakout seasons, and as backups, they are both very sufficient.