i think rios is the obvious choice. he's going to have another war with alvarado soon...he'll be that much more diminished and primed for pacquiao to shine against. in house fight. very possible.
other options include...but are not limited to....
bradley- i thought the first fight could have gone either way. i can see bradley beating him more convincingly this time.
khan- they're both on the come back trail and have been ko'd recently. freddie isn't with khan anymore. they can do a loser retires match.
garcia/judah winner- i think garcia is going to ko judah. i think both beat pac at this point.
peterson/matthysse winner- i think matthysse is going to win this one...but i could see either guy beating pac.
malignaggi- paulie will make pac look bad for about 6 or 7 rounds before pac takes over and stops him.
vargas- easy win and obvious choice since he's an in house fighter like rios.