I've seen Ka/O/Mystere/LaNoubla. I've seen O and Mystere more than once. I would say Mystere and O are best. I like Mystere a shade better, but am clearly in the minority.

If you don't mind separating from your companion, you can standby for tickets the day-of-show. I did this for the 2nd time I saw O and M. You can end up with great seats doing this.

I saw Ka this past Saturday at 9:30p. My show was sold out, but the 6:30p had tickets available for walk-up sale. Doors opened at 8:45 for my show, and it's always best to catch all the pre-show.