Nobody.
Ha, seriously Bones is one of the greatest of all time. Anderson Silva could pose a serious threat (although the age difference is strongly in Jones' favour). Gustaffson matches Jones in size, which would be interesting. And as far as skill goes, Gegard Mousasi is a pretty good matchup. Other than that, Glover Teixeira and Phil Davis are working their way up the rankings, and there's also the potential for rematches with Rashad or Lyoto.
Other than that, it's just going to have to be luck in their favour. I mean, Machida was beating him in the first round and got caught. Vitor Belfort almost caught him in an armbar. And even Chael Sonnen, if could have lasted the rest of the first round, Jon's broken toe would have cost him the title. The most dangerous fights are the ones you're expected to win, and Jones has built up quite the ego, so we'll see. I still think Jon Jones is p4p one of the best fighters we've ever seen
Edit:
To OP: Dude, can you even read??? I named 9 different fighters lmao. it's *beaten* btw. I never said Weidman couldn't beat Silva, but that has nothing to do with Jon Jones? Rashad Evans said the exact same thing too, "anyone can be *beaten* at any given time", and that didn't turn out so well for Rashad. Anyways, my post doesn't have any BS... so idk man, sorry if that's not the answer you were looking for.
Honestly Nobody i mean you can Henderson but he fights just like Rampage and Bones had no problem with him, Machida & Shogun he took out with ease and those guys are no joke, Played around with Rashad. Its a tought weight class but he is just like Silva & G.S.P. he is on another leven than everyone else in his weight class. Unless Daniel Cormier drops down to light heavyweight witch he said he is open to doing i think he could beat bones, since he would have not be as tall but if he throws his weight on bones that would be a problem
The reason why nobody can answer your question here because nobody gives a sh!t about MMA here...Its a g@y sports...
This is boxing not mma
Don't give me no bull ****! Just name some MMA fighters, they don't have to be just UFC fighters.
