I think three years is the perfect spacing between children. It works particularly well if you end up having children of the same sex. My sister and I are three years apart, and have always been close. When we were little, we were close enough in age that we could play together, but just far apart that we weren't interested in all the same things at the same time.
My husband and his brother are less than two years apart, and they have never been close. His younger brother has always been competitive with him, and had a real chip on his shoulder about his older brother. They were on the same athletic team in high school, and that really didn't help.
Our sons are three years apart, and they get along wonderfully. The older one looked forward to the baby's birth, and has loved and enjoyed him ever since (they are going into seventh and fourth grade this fall). They are far enough apart that the younger one doesn't judge himself by his smart, athletic brother's standard, but close enough that they can have lots of fun together.
Then there is the mommy factor. Having two kids close together is incredibly difficult. Having a baby and a three year old isn't quite as hard.
It will be interesting to hear what you decide.