Neutering him will make him a much better and healthier pet. You will eliminate his chance of getting certain cancers and other medical problems. If done early enough, it will stop him from starting undesirable male characteristics like marking. Since he has already started, he may or may not stop after neutering, but many do.
This is a great article about all the benefits of neutering:
http://www.peteducation.com/article....&articleid=911