I join the SPG program as main reward program based on the replies (Thanks for that) and my own experience I had with some properties of the SPG program.
As secondary program I'm not sure which one suits for me. I think I will try out HHonors and Club Carlson.

As Dutch citizen I cannot apply for a SPG, HHonors or any other hotel chain credit card.
I can apply for a standard American Express card and exchange the membership rewards into hotel points. Is it worth it?