with respect to our trusted percysmith, I have a slightly different perspective. If time doesn't matter to you at all, I'd take the 77W. But the difference is slight and probably not worth going out of your way for unless schedule is zero consideration.

I personally think there is definitely a noticeable difference. In the A330: the "triangle" work area between your seat and windows is smaller, while the seat both is and feels slightly narrower (particularly at the feet). Not important but still a "difference" is the seats are aimed slightly more forward in the direction you're traveling. Overall you can really see the difference in inches by checking out the headphone storage area - it's more like a tall skinny storage thing for the A330, whereas it's more of a large cube for the 77W.

I should say I have flown CX quite a fair amount, which is a plus and negative. On the plus side I've sat in those seats zillions of times - probably 30-40x 77W rides in the last year alone (most J, almost all long-haul), and 12+ long-haul A330s in the same period, all long-haul. On the negative side, I'm guessing I notice things infrequent fliers on CX don't notice. I recently flew SQ long-haul, absolutely loved it, and then read some reviews of people nitpicking things about the menu and the F seat on my route I didn't even notice. Note I maybe fly SQ but a few times a year, and this was my first using them long-haul for some time. So just fyi these differences I point out might be really irrelevant.

Also, a very very minute point but both the older-delivery A330 long-haul configs and some of the older 77H's don't have the tiny 1/2 inch rise at the back of your workstation (between your work station and the seat behind you, via open seam between your seat module and the window), which leads to things falling back to your seat neighbor behind you. This problem doesn't exist on all 77G aircraft, newer-delivery A33G/E/Ps whatever they're called, and the newer 77H planes. I think the 77H aircraft lacking this rise were the older 77D planes (an old variant of the 77W which did not have PEY, but had an identical J class), and CX never bothered refreshing J class when they installed PEY, nor when they "refreshed" F. I recently had a round-trip on B-KPA and B-KPX, both which were originally 77A and then 77D, both of them lacked the rise thing in J class. The 77G is guaranteed to have that little half-inch rise.

That said, I can sleep very soundly on both the 77W and A330. The hard product is very good on both.