Any of the Americans really. Probably a little less for Hocker or Koech, just because Hocker already has a gold and I don't know Koech very well. Not rooting against them, it would just be less joyful compared to a win for Brazier, Fisher, Young etc..
A Hiltz win would probably crash the site.
In terms of non-Americans, it's definitely Luis G, given that we now know he was robbed of one by a drug cheat a few years ago.
All of my top choices have already been named, but one I haven't seen mentioned whose win would bring me joy is Jacory Patterson. He has a great story, and the letters j-o-y are in his first name!
Vernon Norwood coming out of nowhere and winning would be the best for me. Dude is always out there and competing and competitive, but he's never won anything big.
Also, Grant Holloway after the season he has had and stamping his authority on the event after all of the doubting.