Arguably it's definitely a try both and pick your favorite (or what you feel like on the day) situation.

I've found the JL F sushi to be very average, although they do rotate it frequently so maybe I've been unlucky. The JL beef curry is pretty good for curry, but it's heavy, not my ideal pre-flight meal. I think the self-serve plates, breads, and desserts/fruits are generally better at CX.
The beverage selection especially Champagne has been downgraded in JL F over the years, to the point I don't think it's that good - in my eyes even AA Flagship Lounges are stronger with beverages - unless the Salon is open, where the whisky served there is unquestionably better. But JL F Salon has very limited hours. Caveat: I am not into sake or shochu, so I don't factor that, although I have to imagine JL F is better there.
The CX lounge is usually less crowded and the staff a bit more personal, in a way I feel the experience there is more premium.