Have to go with Bika. Solid top 10 SMW and if Calzaghe stays in LHW he has a decent chance to grab one of the belts. Forbes is not bad either, he has some good skills but he's pretty much past his prime.
You would probably have to go with Forbes seeing he is about the fight the biggest name in boxing and he had already been a champ even before the series.
Bika is the only guy who could possibly win a world title. He will destroy Mundine if they ever fight.