I have status at IHG, HH, Club Carlson, Best Western and Marriott. Marriott has the best properties, especially abroad. I like their mid-range hotels in Europe and Asia. I stay at hotels only for leisure so luxury is not my priority.
If you are going to spend some nights in Europe, then I think IHG or Marriott will be a good choice, if you are staying only in mid-range hotels IMO. IHG's priority club point breaks is awesome.
If you need to sign up for Marriott rewards, send me a PM and I can get you a referral and both you and I can earn up to 10K bonus.