I've played against both. I'm only an amateur so for me it can be hard to tell the difference. Computer opponents can be set to different degrees of difficulty and style. For example, you can find computers that can play in similar styles to famous grandmasters; the technology is amazing. I would say that the big difference with human players is that they make blunders, i.e., stupid moves/big mistakes. Even at a low difficulty setting, computers rarely make the kind of blunders that humans do. I think that it's more fun to play humans though because those blunders can actually make the game more exciting and interesting. Thanks for the comment,