J class: Go for the Wing. It's large, spacious, has good views of the runway and overall is pleasant. Assuming I had plenty of time, the only reason I wouldn't consider it would be if my flight was taking off from one of the closer gates (say, 1-4, 13-16, etc) because then it's just way too far away.

F class: Toss-up, although the Pier gives the Wing a run for its money. The Cabanas are great and it's bigger than the Wing.

In all honesty, I prefer the J class Wing over F class Wing. Last two F flights I ditched the F Wing and headed to the J lounge. F class Wing feels stuffy and can be awfully overcrowded at certain times during the time (although it is really hit or miss on the crowded status, but sometimes it can be just absolutely packed). Also, they have these TVs that sometimes pax turn up really loud so they blare at you if you're sitting in the main area. Sure, you get food and all...but if you're F already you'll just caviar on the plane if you're going long-haul, and regardless you'll have plenty to eat going forward. Since I've been flying CX really skimps on the wine budget anyway, so you're basically talking about the difference between a $5-$10 bottle in J and a $20 bottle (with some rare exceptions, usually found in-flight) in F. And the J lounge food isn't bad...you still can get made-to-order noodles, they usually have dumplings, sandwiches etc.