If UD seats are not available and I have to choose the LD, there are some very minor factors:

Pitch on row 8 appears a bit better than rows 4-7
If there is a lav queue it will be by row 9
Middle DG block has wider footrests and direct aisle access
Slightly less traffic in the GH aisle than the CD aisle (crew station & UD stairs on the CD side)
Close to door 2L so relatively quick off the plane

Why I prefer the UD especially on night flights:

Quieter, less traffic
Best lav to pax ratio
Side storage

Downsides of UD:

Neighbour
Narrower footspace