Luck very easily. He was seen as a generational QB right off the bat. I think Vick is the only one who came close, because of the different dimension he brought to the table. In terms of QBs I think Winston was huge but nowhere near Luck or Vick's level. Eli was pretty big but so much of that was just the lineage and situation with the Chargers.
After that I think I'd go beyond the 1st pick and put Calvin Johnson next. He was seen as the perfect WR and the expectation was for him to become one of the best of all-time, if not the best considering his physical tools.
Reggie Bush was huge as well but the Texans taking Williams 1st took some luster off. RB is such an interesting position for hype because of the nature of the position changing so much since the early 2000s. You had that wave of backs like Reggie Bush, Adrian Peterson, and Darren McFadden that were all massively hyped, but then it died down until Gurley started to bring it back a bit, even though he was only drafted 10th. But still, I think just with the nature of the position, none of Zeke, Fournette or Barkley were able to match the hype of those first 3 backs I mentioned, even though Barkley was seen as more talented than any of them.
Clowney is the biggest hype I remember for a defensive prospect, even with the fall-off with injuries/play in his last College season. He could have been bigger otherwise, maybe challenged the top QBs. I think it was kind of similar to John Tavares, seen as a generational talent well before the draft, but it became diminishing returns before his name was actually called. Sean Taylor and Julius Peppers were close though. It's weird, even with Von Miller going #2 and turning into what he did, I don't remember as much hype around him, maybe because Patrick Peterson was in that same draft.