Don't think there is any probably about it. In 2010 a poll on Yahoo I think that voted Pacquiao as fighter a year for beating Clottey and Margarito. To put that into perspective, that was the year that Martinez beat Pavlik and knocked Williams TFO :-(
Yaegashi would def be toward the top of the list. HUGE Yaegashi fan here... I still think even with the most impressive W that Yaegashi would be short of several of the other top candidates, but if Sosa gets the W than he honestly becomes probably the most deserving fighter. There are plenty of LW's out there that would beat a 122 pound Donaire. I don't know. Andre Ward won FOTY for beating Abraham and Froch. He won both bouts via decision with minimal action. He also is said to "not be able to draw flies to ____" and his style of fighting is generally seen by the same people who would value star power and punching power as being boring.
Didn't say there wasn't but I doubt any of them would be able to beat him as decisively as Rigo did. Lightweight is at one of it's weakest points in recent memory, take out Uchiyama and Garcia, then so is Junior Lightweight, and we all know Donaire would pose a threat for any Featherweight.
It's unlikely to happen, but if Edwin Rodriguez upsets the applecart and defeats Andre Ward, he becomes a serious factor in this discussion, imo...
I brought that up a few posts back :good Maderna and Grachev aren't exactly bums either, so he'd probably become the leading candidate.
Voted Stevenson due to his surprise blowout of Dawson and great boxing display against Cloud. I expect him to do just fine against Bellew too, to say the least. Overall he has been the fighter that has impressed and surprised me the most, taking all things into account.
Honestly, there is just as strong a case to be made for "Mikey Garcia (if he beats Martinez" as some of the guys on the poll. Salido, Lopez, Martinez is a fine run - especially with Salido going on to capture a world title later in the same year and with Martinez having attained seeming invincibility to losses since hooking up with TR. I'm not sure that is any worse than some of those up for consideration...namely Boone/shot Dawson/Cloud (even tacking on Bellew), Cloud/Murat, and Guerrero/Alvarez.
Voted Rigondeaux, he has the best win (Better than Marquez imo) and not only did he beat him, he dominated the opponent, also, Agbeko is a very decent win too. However, Outside of Kovalev, Hopkins (and maybe Sosa I don't follow the flyweight division) I wouldn't mind if any of them won it.
If Kovalev wins his next fight, he's a leading contender. 4 fights in one year. 3 dominating victories against good opponents. If he knocks Sillakh out, he's right at the top.
I did mention Mikey Garcia (who for the record is my dark horse tip for P4P #1 in the next 3-5 years) on the original post but couldn't fit him in the poll. So he's covered with 'others', being that he was the 10th person to come to mind. I think people will hold the not making weight issue against Lopez against him a little however.
"The fights are too good and the depth of quality fighters is too great" is the only thing I can come up with...