The Co-sleeper and the Crib-sleeper

The biggest difference between my children is where they sleep. This isn't how I wanted it to be, I had envisioned either a huge family bed or them in their own beds.
 I started them both out the same way. For the first few weeks, they both slept on my chest. Then, when they learned how to nurse laying down, they both nodded off with my breast as a chin pillow. I have many many fond, shadowy memories of them that way. Then, slowly I moved them into the mini co-sleeper I have attached to my bed. My son never lasted long in it, so it always ended up being a place to store my water bottle, books, and other things.  My daughter slept soundly in the co-sleeper, sometimes through the night. Nap time, I nursed them both to sleep on our bed, then silently, slinking away I left them there with pillows on either side. At 6 months, I started putting them to sleep in the crib in the nursery. With my son, he would wake up around 11pm , I would get him and nurse then slip into milk-drunk slumber. My daughter would wake, nurse and then proceed to scream for an hour with me on the last nerve by the time she fell back to sleep.
My son has since been in the habit of sneaking out of his bed at night and into ours, oddly in the same routine we had when he was in his crib. When I was pregnant, I tried to break him of this habit. Mostly because he was a restless sleeper and I was worried he would slap, kick, and roll onto the new baby. This worked to no avail. It ended up with several nights of him actually waking completely and then hiding under the dining room table.
I am not a fan of 1am hide and seek.
So, I gave up in favor of sleep.
I had the baby, and things went according to above. Only with her, he was in the bed between my husband and I, while she lay sleeping on the safe side of me. There were a few things that changed quickly. She learned how to roll over quickly and creep. She fell off the bed twice in her trek towards my husbands alarm clock. Then she started being more restless at night, either waking and nursing constantly or just waking and crying. Needless to say, she took to the crib quickly. No disturbances, no snoring, and quiet. So apart from a few nights where she wakes due to teething or gas, she sleeps in her crib. While my son is snuggled up against me every night.
I'm sure this will change when she is no longer in her crib. But only time will tell that.