For the A350. Your first choice is whether you want to sit next to each other. If you do, then choose the middle aisle. The seats here are angled a bit away from each other, but you can still talk to each other easily. If you chose a window seat then you'll be behind one another, and the only real way to talk is over the top of the seats, which requires the person in front to turn around. When your tray table is out this gets quite tricky.
The actual seats themselves are all pretty much as you'd expect. You get a bit more space in row 1, but it's near the toilets so might be annoying. At the back you're next to the loft (on some configurations), which again might get annoying if it's heavily used but it never bothered me when sat in the back row.
FWIW, you can take a virtual tour of the A350 here which might help you decide:
https://flywith.virginatlantic.com/in/e ... -a350.htmlFor the A330 it could be the old herringbone layout or, if you on a A330neo, it's more similar to the A350.