I am the oldest of 5, but my family tree gets complicated. I am the only child of my mom and dad, and each of my parents had two children after me. So I have a brother who is almost exactly 3 years younger than I from my mom, and a sister who is a month younger than my brother from my dad. Then I have a sister who is 13 years younger than I from my mom, and a brother who is 13.5 years younger than I from my dad. Try explaining THAT one in school lol.
I think the 3 year age gap is just about perfect, both from a sibling and a parent point of view. Close enough to be friends, in the same school, etc, but far enough out that the older is probably potty trained, can eat on their own, play, etc.
My daughter is almost 4 years older than my son, we'll see how well it works, he is only 4 months old now. So far though, she is just old enough to want to be helpful and still be pretty independent. She can put her own movies on, get silverware, put things in the washer, etc...and still be young enough to want to do it, lol.
Dez