Honestly, I have also flown JAL in CX in Y and I vastly prefer DL. Every time I've flown JAL and CX the cabins have felt like saunas, while DL keeps the cabins freezing (which I prefer). 2nd, JAL and CX don't give bottled water to Y passengers, just from the tap which I will not drink, while DL gives unlimited Evian bottles to Y passengers. Lastly, JAL and CX provide much less food compared to DL, I always leave JAL and CX hungry while I am fairly full on DL. In J its a toss up, love that CX gives espresso (JAL only serves it in F). DL bedding and deserts (ice cream sundaes ) are much better than both CX and JAL. Unfortunately, the hot cabin issue on JAL and CX is also true in J.

Edit: entertainment is also much better on DL. Though after flying CX many times I know which merchant bank to use in HK