I will be taking a China Eastern flight from YVR-PVG, plus some other China domestic flights. I typically don't take many Skyteam flights so I haven't registered in any of their programs (being based in Canada, I usually end up on Star Alliance carriers), but I figure I would take this opportunity to do so. So my question is in which program should I register?

I am not sure what my future travel plans might be with Skyteam, but my thinking is that I should register with Delta Skymiles since miles there won't expire (correct me if I'm wrong on this), but I would appreciate any suggestions anyone out there may have.