Is there any quality or durability difference between metallic and non-metallic car paint? Or is it just an aesthetic choice?
It’s just aesthetic choice.
No durability difference. Metallic may be more difficult to get a good match if you need a repair. Today many of the paint shops have some really good pros who can do a very good job of matching however.
Most paints these days are covered by a clearcoat. This layer provides the durability.
Perhaps it would help to point out that metallic paint is only translucent paint with the inclusion of ground up mica particles giving it a glittery metallic look.