Depends on the mood- I often select specific albums- today has been "Get Lucky" for example- but in some moods/circumstances I'll opt for a playlist. If I'm going on a long drive, longer than a single album, rather than fumble about changing albums I'll set a playlist going that I know will be long enough to see me through to the end. Or if we have friends round for an evening, a good mixture playlist can keep everyone happy through. I've also got a playlist of gentle stuff which I think of as my "morning after the night before", nothing too loud if you get my drift...