It's likely recency bias. We've seen a lot of Jaelen the last year and nothing of GR15 so memory starts to fade! Personally, I'm with you . . . I think Greg is the better prospect and has a better NFL career.
Watching those clips, he seems to have a great feel for when to disengage a blocker and attack. I think he's a smart football player with freaky length that will have a very, very productive NFL career.