I would second the Bristol in Vienna and add the Imperial in Vienna as well.

The Bristol is dear to my heart because my Mom and I were upgraded from a Penthouse Jr. Suite on a SPG points reservation for 2 nights to the Prince of Wales Suite. Oddly, when my Mom saw pictures of the PoW Suite during the planning stages of the trip I emphatically quipped "Don't worry Mom, we won't be staying in THAT room!!" So, in Vienna, I was eating my words -- thankfully the cakes and pastries are so good I didn't mind!!