I never actually TTC! When DD1 was only 9mo, I found out I was 6 weeks pg- at that point, I basically had three options: wean, abort, or nurse while pg. I chose the latter.
It was really, really hard. It was hard to care for a crawling baby/young toddler while pg. It was hard to care for two babies at once. I really wouldn't recomend that kind of spacing to ANYBODY, not unless you have a lot of help (so you can take a nap when you're pg and tired and literally need more sleep per day than your crawling baby.)
I didn't really enjoy DD2's infancy, as I was so overwhelmed. When DS was born 5.5 years later, I enjoyed him a whole lot more. If I was actually planning when to have children, I'd space them several years apart. I think waiting until your older nursling is ready to wean, or at least until he or she isn't nursing very much anymore (say, a 3yo who's nursing 2-3 times a day) would make your life a lot easier in many ways.
Now that they're bigger, I have some perspective on the whole "kids close in age will play nicely together" aspect. IMO, that really doesn't compensate for the extra work of having two babies at once. When they were toddlers, they played together nicely, but they also both needed a lot of intense mothering and it was exhausting to care for them both. When they were 4 and 5, until they were about 7 and 8, it was nice that they could play together and have a lot in common.
But ever since DD1 was about 9 or so, it got hard again. They had different friends, yet they were close enough in age that DD2 felt very left out and insulted if she wasn't included. They've mostly outgrown "playing together" and they often do not enjoy the same activities. DD2 is as likely to spend a few hours playing games with DS as with DD1.
And if you want to look at adult sibling relationships, you can look at my mom and my aunt- 14 years apart in age (yes, my mom was a teenager when her sister was born) and they're currently the best of friends and see each other at least once a week. Or you can look at my brother and I, 14 months apart (little more than a year; one grade level when we were in school) and I see him once a year, piggy-backing on visits to our parents. He's practically a stranger.
I've met my 2yo neice twice and my 4yo nephew 3X.
So, I had several years of feeling pulled between the different needs of 2 babies/young children and felt incapable of meeting both their needs. Then I had a few years when they played together nicely, and required less adult interaction because they had each other. Then I had two adolescents with distinct personalities, who probably wouldn't have chosen each other as friends if they weren't sisters. I doubt their current relationship would be much better, or much worse, if they were further apart in age.
Right now it's kind of tough because DS is 7 and doesn't really have any playmates in the family. But, as soon as it gets nicer out, he'll spend a lot of time playing with neighbors around the same age. Dealing with some 7yo boredom is a lot easier, overall, than trying to balance the needs of an infant and a toddler or two toddlers simultaneously.
