They'll have very different roles in the NFL. Why was Kupp drafted first? He's more pro ready, an easier projection, and better at this point in time. Reynolds is a deep threat as it stands now. He's a long-strider who can win in the air. He has the change of direction skills to be a legitimate threat in the intermediate range as well. He'll need to continue to develop as a route runner. He has a thin frame, and that won't change. His big issues early on will be adapting to a much more complicated scheme, getting off the LOS against press coverage, and winning in the short passing game.
As it stands now, his releases are a bit predictable. He has the quick-twitch athleticism to really develop there. But with his thin frame and play strength issues, it'll be tough for him early on. He's competitive, though. He's a long-strider who doesn't have a lot of suddenness in the first 10 yards. It'll make it more difficult for him to separate underneath. That means he'll have to produce using his frame and ability to win at the catch-point. Reynolds has a lot of the same limitations that Alshon Jeffery had coming out. I want to make clear that Reynolds isn't Alshon, but his game is somewhat similar. If he's going to win underneath, he'll have to do it by using his body and catching it with a defender on him. However, he has the build-up speed to climb over the top of defenders and win 1-on-1 down the field. Alshon had better hands, a bigger body, and more strength/physicality. Reynolds changes directions better and has more upside as a route runner. Reynolds is probably more of a #2 WR if he develops the way I expect.
In regards to Kupp, I've spoken about him ad nauseam. He lacks that extra gear to separate vertically, but he has everything else. And he might still find a way to be a deep threat. There are a lot of guys who win vertically in the NFL without using pure speed. Kupp may be a #1 WR, a #2 WR, or a #3 WR, but I feel confident that he'll consistently produce.
I had Kupp as my #1 WR on Day 2. Reynolds was my #5 WR on Day 2 (#1 on Day 3).