It's not a hard decision for who you should make first. Starscream. Not my first choice but makes sense from a company point of view. He's a popular character, it means you can keep interest high by not jumping straight into the big two (Optimus and Megatron) and it also gives you the opportunity for remould/repaint to pump out the other Decepticon jets cheaply. Oh he also has a built in exclusive, with swap in Coronation parts...
Then you have
Skywarp
Thundercracker
Dirge, Ramjet and Thrust
Other characters that are easy remoulds into other are Prowl, Bluestreak and Smokescreen. Also, Sideswipe into Red Alert.
My most wanted is Beachcomber. He could have a switch out hand (gold and normal) and switch out weapon (normal gun and stolen golden seeker rifle)
however overall it would be nice if we see a couple characters that haven't been done a thousand times please. Something like Sky Lynx would be pretty awesome