We didn't co-sleep. Ben slept in a co-sleeper until he was around four months, then we moved him to his crib in his room. (For those of you who haven't geared up an infant in the last ten years, "co-sleeping" is putting the baby in bed with you, and a "co-sleeper" is a bassinet with three sides that attaches to the side of your bed so the baby is in reach but not actually in bed with you.)
I'm not philosophically opposed to co-sleeping, but it wasn't an option for me for a couple of reasons. One, I love pillows and blankets, and the recommendation for safety when co-sleeping with a newborn is not to have either. It seemed to me that the comfort offered by co-sleeping would be significantly reduced by stripping our bed. I didn't relish kicking out the dogs, either. Also, I like very much to read or watch TV in bed. At some point, I assumed, this child would be going to sleep before 9:00, and what was I going to do, headphones and booklights? This is my time to unwind, and the furtiveness would have bugged me. Possibly the biggest con for me, though, was the stories I'd heard of people trying to get toddlers or big kids into their own beds and having a hard time with it. Discipline and making big, uncomfortable, "for-your-own-good" transitions are so very much not my bag. It seemed easier, even during the hell of a sleep-resistant infancy, to buck up and Ferberize rather than buckle and co-sleep.
I had friends at the time who were co-sleeping, and whose babies (and therefore whole families) slept great. I envied them their rest. Now, though, while Ben reliably sleeps through and requires at most a brief redirect (usually a cuddle in the rocking chair), most of those kids are having a tough time with the transition to their own rooms, which in a few cases corresponded unfortunately with the arrival of a new sibling. I also know former co-sleepers whose transitions were seamless, though it seems less common, just like I know families who transitioned to a crib and sleeping through without incident. (I should say I'm more or less conflating co-sleeping with other forms of not sleep training. If you, say, lie down with your toddler in his room for an hour so that he can fall asleep, I'm lumping you in with the co-sleepers.)
So it seems to me that it's a trade-off. At some point, presuming you eventually want the child in her own room, she will need to learn to put herself to sleep there, and put herself back to sleep when she wakes up there. No matter when it happens, whether in infancy or later, it is a tough lesson to learn, and it's tough on the whole household. I think you should do what works for your family, but it seems to me that there's a positive benefit to getting this unhappy stage over with sooner rather than later, especially if another baby is going to enter the scene.