Las Vegas Fine Dining
I've now been to all but Picasso of the Vegas' "top tier." Ranking them, I'd say The Mansion of Joel Robuchon BARELY edges out Guy Savoy for best overall while Alex lags behind by a bit in terms of presentation and service. The food at all three are great.
I personally quite liked MiX and Le Cirque, as well.
Having not been to any on your list, I'd go with L'Atelier.
I absolutely agree that Alex is the best of the best. You won't be disappointed if you go there. We've been to Picasso a number of times over the years, and it is very good, but not as good as Alex. Le Cirque in the Bellagio used to be our favorite for a number of years before we tried Alex (I guess actually before Alex opened), and is also quite good.
My favorite fine dining restaurants are: Alex (Wynn) and Le Cirque (Bellagio). Actually, I never miss an opportunity to dine at Alex. In fact, I schedule my trips to LV to make sure that Alex is open for dinner when I'm in LV. Alex is open only Wednesday through Saturday (sign of the times). Yes, Alex is that sensational! I dined at Picasso about seven years ago, and I was underwhelmed with it. Same for the Joel Robuchon restaurants (dined at the Mansion two years ago--haven't rushed back). I live in NYC, and have dined at L'Atelier at the Four Seasons, and while it was very good (even met Chef Robuchon), I haven't rushed back either.