I've read that from a health point of view for both the children and the mother (according to WHO and some other organization that did a massive study), 3-5 years apart is the ideal spacing. Also, my sister and I are three years apart, and are best friends to this day. Accordingly, I left my IUD in until my firstborn was a little over two. We have kids who are a little over three years apart, and it's worked really well for us. One of the great things about it is that I had over two years to focus on just learning to be a parent and getting to know my oldest. On the other hand, my kids are close enough developmentally that they play together really well.
Another fringe benefit is that I didn't have an awful lot of time handling two kids in diapers at once. My older one potty-trained himself shortly after his sister was born. If I had had them closer together (as I was tempted to do, but I made myself wait), I would have had a lot more diaper action all at once.
I won't say adjusting to having two was easy for us. It was tough. However, unlike the previous poster who said it's taking a long time to get easier, I've gotta say it's been comparatively easy since my little one learned to walk! (Sorry to those who are still having a rough time
Good luck deciding!
Tandem-nursing VBAC mama to Thales, 4 1/2, and Lydia, 1 1/2