Your choice, eventually, will be based on which engine you want to use. If PLAY, then in the future, you'll be targeting East West products. However, even with their upgrades, PLAY still has problems, not to mention complains about their lack of support.
Of course, there are other choices - VSL (Vienna engine), Kontakt, Garritan (Aria engine) etc. And you can use more than one engine simultaneously, although that will not be the most efficient if you are running only one PC with lots of instruments loaded.
I can't remember much about the offer. It was in the email, but I deleted it. Probably not the complete composers package. If there's no offer at their website at the moment, do wait for Christmas. Also, their Hollywood Strings will be out soon, although I doubt it will be part of the Complete Composers package as it will be priced much higher (more than $1000 USD).