We had a second-hand Bjorn, a pocket sling, and a Moby. My DH occasionally used the Bjorn because (in his mind) it was simpler to use than the other carriers. I used the pocket sling very early on with DD and it was great for those growth-spurt periods when she nursed _endlessly_ -- I could get her in there and she was able to nurse while I had my hands free to use the computer, walk around shops or town, or (sort of, one-handed) push around a stroller, if we were out and about.
I used the Moby the most, but when DD was teeny she wasn't a big fan of being shoved in there (you have to tie it on you first, then slide the baby in one limb at a time). I also found it awkward to get her out if she fell asleep in there, and I often didn't want to let her sleep in there because I was HOT from (usually) walking around with her in there and I needed a break. It also got very little use early on because DD was born at the beginning of the summer and it was just too hot to have that many layers of stuff. Hence why we bought the pocket sling. When she was a bit older, I used it a lot when I helped out a friend for our weekly babysitting trade - -her daughter, the exact same age, would ride in the stroller and I'd put DD in the Moby and we'd be off walking around town. The Moby did feel really secure, though, and it was the most versatile of all of the options. We last used it when DD was 18 months and she wanted to be carried around London when we were visiting there -- so we did the back carry with her for a bit. But she wasn't really used to it, and so we didn't use it a lot that way. I'm sure if we'd used it more frequently it would have been even more helpful that trip, and we probably could have used it a bit longer.
I borrowed a ring sling on occasion when DD was going through a horrible period for a couple months of teething and needing to be constantly held and rocked to sleep (4-7 months or so). But she hated being squished to be put into the pocket sling or Moby. The ring sling made it easy to get her in and comfy without squishing her too much. Consequently, since I'm expecting baby #2 this fall, I'm making my own ring sling to add to our complement of carriers. :)
All this to say, I guess, some babies will be happier in some carriers than others, and some babies won't care as long as they're close to you. So be prepared to try different things, borrow things from friends, if something doesn't work for you.