Under the present COS you will join the freighter fleet for a set period (3 years from check out I think). If you end up on the Classic you will not be stuck on it as the Company will move you after the requisite period. If you are looking to move companies then perhaps the 400 is the best choice as there are always jobs for 400 FOs. If you want plenty of hands on flying then the Classic is a definite attraction. If you want early command and you are up to to it then the Classic is the way ahead, if you are not bothered and want to go to HKG then go for 400F based in CDG.
Hope that helps