And they need that. They haven't really had that guy since Faulk.
To me, the best scenario is to have diverse "types" of receivers. You need your speed demons. They can be smaller, but they need to also have great hands. I think Austin's real deficit is in the lack of reliable hands. He has all the other traits you want for your speed guy, which means the Rams should keep looking. Though I do have to give Austin props for toughness. Throughout his career, he's been fearless for a guy his size.
You also need your big receiver, with hops, solid speed and the ability to win toss ups. Perhaps Reynolds is that guy down the road. But, as mentioned, I'd like the Rams to look to Hemingway for that.
Kupp represents the slot guy, the possession receiver who has sneaky athleticism and can lull DBs and linebackers into mistakes. He has better than average size for the position, but it appears the thing that sets him apart at that spot is his football IQ. The Rams need that more than most teams.
I don't know what to make of Cooper, really. In some ways, he seems like a poor man's Austin. Not as fast or as elusive, but better hands and a bit more size. We'll see. The Rams probably need to make a choice between them soon.