I've been using the Boba with my now eight month old, after having gotten it when he was seven months. It is possibly the most comfortable baby carrier that you can buy. I didn't even feel like I was wearing the baby when I had it on. I felt close to him, cuddly, etc, but I didn't feel like I was carrying his weight at all.
It's great for both a front or a back carry. Either way, I hardly feel like I'm having to carry him. The back carry is very comfortable and makes it easier to cook or get things done.
I now prefer the Boba to the Ergo (which I also have). The fit is better for me and the top buckle feels more snug; it always seemed loose on the Ergo.
My only real complaint is that I don't like trying to nurse in the Boba, so I end up unbuckling the top buckle and arranging baby to nurse, then putting him back on when he's done. With a sling, I could just nurse him and not have to fool with it, though the Boba is more comfortable than a sling.