At least in the front of the plane, I find the A350 to be noticeably quieter than the A330.

And if seated by lavatories or the crew areas/galleys , that difference can be a good thing or a bad thing, depending on how sensitive you are to noises.

I definitely prefer the A350 to the A330 when flying SAS.

Maybe it’s just me, but sometimes I find the A330 business class seats to feel more comfortable in semi-upright seat positions than the A350 business class seats in semi-upright seat positions. For sleep, I find the A350 better.