Is Josh Thomson, in my opinion. It's probably not a match-up we'll ever see, because of Josh's inability to stay healthy and his lack of solid win streaks, but I think he has the style to give Bendo fits the way Frankie did.
He has a technical kickboxing game, and has great hands when he fights disciplined and doesn't brawl. He's got a great chin, and good offensive and defensive wrestling. He's fast as hell, and while I can't recall his bottom game being particularly note-worthy(not like Diaz or Cowboy), he scrambles well and gets back to his feet.
He also seems pretty strong at WW, and wouldn't be manhandled the way Diaz was or outsized the way Edgar was. I'm reasonably sure that Josh and Bendo have pretty similar heights and reaches as well, I think they're both about 5'9".
I could be completely wrong, and I do think Bendo would still win and might even win impressively, but I can also see Josh giving Bendo many of the problems that Edgar gave him in the 2nd fight if he were to fight a very disciplined fight. 
Haven't seen too many of his fights, but does he have the cardio to keep up with bendo?
Shakes head 
I agree.
Ben would wreck Thomson.
The correct answer is Jose Aldo once he moves up
JShad - Haven't seen too many of his fights, but does he have the cardio to keep up with bendo?
His cardio is kind of inconsistent. Against Kawajiri and Noons, it didn't look all there. Against Melendez(particularly the 3rd time), and against Healy, I thought it looked fantastic. Really I think it depends on the kind of injuries he's suffering in his training camp.
WestCoastMXC - *Shakes head*
Anything you'd like to point out wrong with what I said? People are saying Melendez could beat Bendo and that he is the # 1/2 LW in the world.... And Thomson arguably beat him 6 months ago.
Grey Maynard
GayGuardMooseSaucy - Ben would wreck Thomson.
The correct answer is Jose Aldo once he moves up
Not sure I agree that Aldo will ever be the threat at 155 that he is at 145. Similar to how I feel about GSP potentially going to 185. They both added a lot of muscle to their frames, and it slowed them down and hindered their performances. Both(particularly Aldo) looked leaner in their most recent fight(s) and were much more impressive.
AresSmashedPrahjuhdee - Melendez
Melendez and Thompson could both give bendo troubles
Pettis :)
TheMentalisT - I don't see Bendo taking down Alvarez that much and that would cause Bendo to stand with Eddie. Alvarez could easily squeak out a decision
I agree with that. I think that fight could really come down to Bendo's cardio and which of them has the most significant moments early on. If one of them never allows the other to find their groove... Either guy could get finished or lose a decision.
I think Alvarez fades late a little bit though, and I can't think of anyone he's faced recently as relentless as Bendo, aside from Chandler. And Chandler finished him late in an absolutely ridiculous fight.
The worst?
JDS or Jones.
Honestly I see Bendo going on a GSP-like run over the next few years, he improves at such a quick rate , is so dedicated, and is so physically gifted that its gonna be an enormous task to take his belt away.
Thomson is just the guy who I think matches up best with him, from what I've seen(with the exception of Edgar)
aldo, josh, gil and maybe pettis again.. imo
I thought he beat Gil last time but I don't agree
Alvarez, Pettis, Melendez have the best chance to beat him.
Aldo and Gil
Footwork, combos, wrestling will beat Bendo.