Gutters are the obvious suspect
A leaking joint or overflow can keep the face of a fascia wet. Check brackets too; a gutter that has dropped out of fall may hold water against one section for long periods.
Water can come from behind
This is the part easily missed. Damaged underlay at the eaves can discharge onto the rear of the fascia. The outside may not look especially wet until decay is established.
Soffit staining
Brown marks on a soffit can be from roof water, gutter overflow or even birds and nesting debris. Follow the staining back rather than assuming the soffit itself is defective.
Replacement materials
Timber and uPVC both work when the roof edge is properly detailed. The material choice matters less than keeping water where it is meant to go.