Most favourite would be Kovalev v Stevenson, but I doubt many casuals would rush for PPV even though it could be a fight of the year I suspect it would have to be the HW's -Wlad v Wilder Khan v Cotto @ 154lb Froch v Hopkins Frampton v Santa Cruz
With HBO applying the pressure I'd say there's still a very solid possibility of Canelo-Cotto occurring around abouts the end of the year. That's the biggest fight to be made right now not involving Pac or FMJ (not saying best, just biggest in terms of box office).
In the UK it would be any of these four - Froch v GGG......Khan v Brook.....Frampton v Quigg.....Fury v Klitschko. On the World scene......Canelo v Cotto.....Stevenson v Kovalev....Wilder v Kiltschko But no fight is going to match Mayweather/Pacquiao for a long long time!
if they both win world titles, I'd add degale vs groves too, and possibly degale vs froch. can't believe nobodys saying brook vs gavin:deal