My personal choice would be Mike Wallace.
There are a lot of criteria that should be kept in mind.
In this regards, Mike Wallace makes the most sense. We don't have an elite speed WR who can stretch the field and open the underneath routes for our TE and slot receiver, and pull a LB or S back from the line of scrimmage to make things easier for Lynch.
Also Wallace would play to our QBs strength of a cannon plus arm, and our team's offense would have the capability of striking from anywhere on the field.
Out of the four FA WRs mentioned, Wallace is the youngest and freshest, followed by Bowe, then Jennings, and lastly Welker.
We don't want a WR who has a lot of mileage on him, it's safer for us to go with someone younger.
Not much to comment, Wallace is the winner here.
Order from tallest to shortest is Bowe, Wallace, Jennings, then Welker.
Bowe wins (with Mike Wallace second).
I think the QBs for these FA WRs should also be taken into account. Try to look for the WR who has done the most with the least help/talent around him. If we talk about elite QBs then we should take out Welker and Jennings, since Brady and Rodgers respectively were throwing to them. They are most likely to have benefited from phenomenal QB play.
And if you look at it there is truth to it. Jennings was out and Rodgers was able to keep the engine running quite well without him, throwing it to Jordy Nelson, Randall Cobb, James Jones, and Jermichael Finley. Same with Welker. Even when Belichick was sitting Welker in favor for Brandon Lloyd, Julian Edelman, Aaron Hernandez, and Rob Gronkowski, Brady was still keeping the offense rolling. It wasn't until alternating injuries to Hernandez, Edelman, and Gronkowski that Belichick was forced to go back to Welker.
On the other hand, Wallace had only a good, but not elite, QB throwing to him on an aging team with less offensive talent compared to the Patriots and Packers. Bowe had a mediocre QB throwing to him on a horrible Chiefs team. Wallace and Bowe had success with less going for them the last few years, so in this category Wallace and Bowe would win.
Wallace and Bowe win.
Quality of Opposing Defenses:
Next we should probably consider the strength of the passing defense these FA WRs have had to face, and mostly focus on defense within their own division since that is the only constant year in year out, plus they play 6 games against divisional rivals every year.
Now I don't want to type it all out, but in my personal belief Wallace (AFC North) has had to face stronger defenses overall the past several seasons compared to Bowe (AFC West), Welker (AFC East), and Jennings (NFC North).
So all, in all, I think the obvious choice would be Wallace here. Now I know that you can't 100% accurately predict a free agent's success on a new team based on only the above criteria, but I think it does lay an argument and statistical likelihood for a particular player over another. And in that case, I believe it is Mike Wallace.