I disagree, SQ used to win hands-down, but for this year (2002) on my flights they rate well behind CX for in-flight service, and even further behind for ground service. SQ has cut spending a lot on food (maybe in half is my guess), and I have had a broken F seat for 5 flights in a row (and SQ thinks that is normal). It is a great seat when it is working, but too complicated to be reliable (CX seats have a manual over-ride, for example, so they still work even when broken -- but I've never had a broken CX seat yet).
In the past month I've taken 6 CX, 4 BA and 2 SQ long-haul F flights (over 7 hours; that seems to be the boundary for service level offered). In this sample, CX was a clear winner and had very consistent service. They were also able to handle a complicated ticketing change graciously (their F ground service is every bit as good as BA Special Services, for those who have discovered what that is). The food was of much higher quality than SQ (for the same route, HKG-SFO, so it is a fair comparison). The Kaiseki service (offered on a few Tokyo flights) is phenomenal for an airline, and better than the JAL F meal (in fact better than many Tokyo restaurants). The caviar is generously served and higher quality than SQ (or any other airline). Cabin service is good on all 3 but friendlier on CX; BA is a bit variable but can be very (very) good. SQ seems to have a morale problem this year.
It is a bit unfair to compare the airlines based on a few flights, as their equipment varies so much within type (for example, just on the 343s CX has 3 different F seat types, and 2 on the 744s).
BA (with a larger fleet) has even greater diversity in seat construction. The newer CX seats have (partially) fixed the problems of the older design, for example there is less flex in the newest CX seat. Also it has a movable armrest (a big advantage over the BA fixed design).
There has been a lot of change in F service this year, and SQ is fallilng, BA was falling but is now rebouding back, and CX is rising. I think it has a clear lead. I have the impression that CX does a lot of training for their staff and does a much better job of it than other airlines. They show a passion for their work, ingenuity in solving problems and grace in performance. And this behaviour is systemic -- something that I cannot say for many other airlines.