Depends on your gaming style i think between these two, These are my opinions
Dead Rising is more of a fun, relaxed and time killing game for when you're bored or just want to hack'n'slash zombies with anything you can see really.
Left 4 Dead to me is a bit more serious due to having to work together to make it to each safe room or to stop the survivors making it to the safe room as the infected, Overall L4D for me is better due to multiplayer which makes the experience different due to peoples playing style, I like both games though