This question will be a lot more interesting in 12 months time, maybe even two years but right now I would say: Haye Khan Froch But really hard to seperate them for me, all have weaknesses and all have strengths the others don't. All of them still await there biggest tests.
Froch, what he has achieved in the past year or so beats both of the other 2, Haye will probably overtake him though if he can beat (which I think he can) either of the Klitschko's.
I wouldn't say its the Froch lovers posting, it seems to me there are a lot of Froch haters. He's a better operator than Khan and I think if he was with FW and not MH then more people would be loving him. Having said that Haye is now two weight champion, he put it on the line and had he lost he'd be bottom of this list, but now he's top. Thats how it goes.
To the people who say Kahn will acheive more than Haye. Kahn will never unify a division and then move up in weight and win another world title (Who know's though), although I wish him the best. Haye's skill/acheivement's surpass Kahn and Froch.
Haye's already beaten him, he unified the Cruiserweight titles (I know he's been inactive but the question wasn't about who's done better in the last year). That alone beats what Froch has done I think, let alone winning the World Heavyweight Title, becoming a 2 weight world champion.
Interesting depends on criteria, but based on achievements in career Haye, Froch and a fair way back Khan. To be fair to Khan he's got 6 years or whatever on the other 2 to make up the gap, but if Froch wins the Super 6 and Haye beats Vitali and/or Wlad then it would take a move of promoter I suspect for him to have any chance, let alone ability.