Here's my top 3:
3. Ratchet (2007): This mould is 10 years old now....He needs and upgrade. BAD.
2. Megatron (2007): From what I've heard from some fans, it seems that Hasbro did not do Megatron's original movie form justice when it got the leader class treatment. With the technological advancement of toy production 10 years after the first movie, I belive Takara and Hasbro have the potential to breathe new life into '07 Movie Megatron.
1. Blackout: He was the biggest Transformer in the 2007 movie, with a cool design to empower this characteristic. The SOCCENT Base attack was a prominent example of how he was depicted as an imminent threat, back when human firepower could only make a small dent. While his voyager figure was average, it failed to capture him in a larger scale. HE should've gotten a leader class figure instead of Brawl. This is definately an oppertunity to do Blackout justice, to make us relive the first time we saw Michael Bay's Transformers come to life in that second teaser. It's a oppertunity I hope Hasbro and Takara do not miss out on.
Honerable Mentions (They should get the masterpiece treatment too): Barricade (2007/2011), Brawl, Jazz, Ironhide, Bonecrusher, Optimus and Starscream Protoform (I know most would probably think that it's a stupid idea but I'm kinda interested), Starscream (2007)