depends on the mood. i use Spotify and i have 4 major playlists:
1. hateful and heavy: ********, death metal, extreme music - Hatebreed, The Black Dahlia Murder
2. loud bikes and smoking pipes: "motorcycle" inspired music - The Sword, High on Fire
3. jammin' R&R: 90s Alt. rock and metal - Bush, Local H, Sound Garden
4. smooth mix: 90s-00s chill rock and metal - HIM, Alice In Chains, Flaw
of course, each playlist has more artists than listed! and if none of you use Spotify, i HIGHLY recommend it over Pandora. much better service with a lot more features.