All very interesting, but I would likely to know your reasoning, particularly in the case of the various Grand Duchesses I don't know much about.
For myself, it has to be the Grand Duchess Olga Alexandrovna, on the basis that she was practical and down to earth, coped with a great deal of tragedy and managed a happy (second) marriage.
I rather like Xenia Alexandrovna too, but she had no sense where money was concerned, and from what I read in John van der Kiste's biography, she allowed her sons to live like drones rather than sending them out to find jobs.
Ann