For me it is a bit of both - when I was just dealing with severe depression and anxiety, before the memories returned and I was diagnosed with PTSD, I definitely listened to a lot of darker music: more depressive hard rock, or brooding music, or extremely sad classical/film music. But after being diagnosed with PTSD I usually just can't handle that type of music for long periods of time - it's too dangerous for me to get sucked back down again. I suppose I've also learned to be more proactive about coping strategies and that includes putting on lighter, happier music. I still do love my dark music, but it's not healthy for me to be listening to right now.