I dont see how anyone could really pick Dez over DT.. or atleast say its clear cut.
1) DT is still learning the art of route running.
2) He is finally getting NFL ready, what i mean is he is bulking up but in the right way, he is getting to finally practice and do things in the offseason that he previously never was able to due to rehabbing from injuries.
3) He has talent around him that will not allow Defences to really just single him out as the guy to stop, while being the #1 will not be able to be focused on like Dez will be.
4) He is naturally bigger and Faster... you combine those with getting better in all other WR areas like routes and stuff he will continue to blossom.