I had mine 1 year and 3 months apart. I would not suggest that again. I feel like I never leave one stage before the next starts. I would say at least 2-3 years between children. My oldest reverted to habits he grew out of when the baby was born. I couldn't get the oldest potty trained until the youngest was well on his way to potty training. It's a bit unnerving when you think you just exited the terrible two's and you enter it again with the next at the same time. Ugh. So many people say they look like twins. Honestly, I think it would have been easier if I had twins.
Additionally, your body needs time to reach it's normal hormonal state after having a child. I had many complications with the second partly because my body wasn't back to pre-baby state. I looked just as thin and healthy, but my hormones, uterus, and other things were not there yet. My body wanted to have the second baby at 6 months. I was 4 cm dialated. I had to go on bedrest for months. That was rough. When baby finally arrived, I had him in 2 pushes. He practically fell out, which is scary looking back that I could have had him at home or the street.
I know every woman is different, but that's what I experienced. I think it's nice to have more time to establish your relationship with baby number 1 before the next comes as well. Have time to establish family routines, make sure the relationship with hubby is strong. Things change so much between being with your partner and then adding a baby or two. Sometimes you don't notice it all at once, but over time you realize you might spend less time doing things on your own, things with your partner, things developing your relationship. Day to day becomes focused on the kids. When the stress of raising kids, finances, health, or other things come up, the relationship between the parter and self is what holds things together. That should always be strong throughout it all.
Take some time out with hubby or your partner and make sure one-on-one time is a part of your normal routine as well. Sometimes I miss the dating, feeling special because you're on a date, having the time all about the two of you.
-S.