For me, it depends.
If I'm playing a game, I'll probably go with some arctic monkeys, strypes, death from above 1979, dead weather, and black keys. Or at least a playlist that is generally rock based.
If I'm working on a project/studying I seem to enjoy more math rock type playlists that include stuff from Giraffes? Giraffes! or LITE. I suppose it's easier for me to concentrate when the music has no lyrics and has a faster tempo.