4 class:
- Sat further back so longer to get off
- Sat behind the engines so noisier
+ 32H/K are the best PE seats across the fleet
+ Toilet in the cabin
- Front row has a lot of legroom but will be used as a crossing point to the toilets by other passengers

3 class:
+ Quieter as over the wings
+ Smoother as over the wings/COG
+ Less likelihood of economy passengers sneaking forward to use the toilet
- You have to use the economy toilet

I've flown CX PE dozens if not hundreds of times and I have yet to really notice any difference in service between the two to the point where i prefer one over the other.

If I can get 32H/K on the 77H I will take that, otherwise I probably prefer the 77G.

I have not yet flown PE on the A350, although the aircraft itself is very nice.