That's a tough one. Brees and Carr are about equal in my opinion. Gurley, Landry, and Cooper should all improve their fantasy points as the season progresses. Walker is likely to give you about what you've seen so far. I guess it would depend on your team need and how your players are required. Is a tight end required in your weekly set? If so, do you have someone who can adequately replace Walker's point production?
Let's look at it this way. Brees/Carr wash. Cooper/Landry wash although I'm sure there are guys on this board who would think Cooper has more upside. Gurley/Walker. Gurley has disappointed but I would think that his numbers are likely to improve. Walker is what he has shown. Another consideration is that Tight Ends seem to get hurt at a disproportionate rate to other skill positions. Maybe that's a reason to do the deal.
Tough one. Good luck.