Sorry I seemed to fall off this thread. The baby bjorn we have is this one:
www.babybjorn.co.uk/baby-carriers/baby-carrier-one/?gclid=CK2TuOTEos8CFegp0wodUOECSg
It has zippers that allow you to adjust how the legs sit, they can "hang" or they can do the ergonomic M shape I think it's called, ie the knees bent round the adults body not hanging. If you click through the pics on that link you will be able to see what I mean about the leg shape. Baby bjorn have done lots of research into this and hip dysplasia and this model (I can't comment on other BB models) is approved by the hip dysplasia association. I'm quite passionate about this and quashing incorrect info because a relative has a baby with hip dysplasia and this was recommended for them by a specialist.
Leo there were various reasons I preferred a structured carrier to a wrap - my baby was born heavy so only the strongest wraps felt secure enough but he was a summer baby so these were very hot. I found it difficult to manoeuvre the baby in to the wrap, I tried both tying the wrap then putting him in and holding him against me and wrapping and both were cumbersome when you're out and about. I found the carrier had longevity - used the wrap for about 4 months max, still using the carrier for back carry at 16 months. I also had an emergency c section so the waist support of the carrier worked better for my scar, and I personally found the padded straps and structured waist better for my back too.
The reason I preferred the BB over the other structured carriers I bought and quickly sold on is that it's really easy to do up, some of the others - eg ergo brand - have a clip to do up behind your shoulders which I struggled to do up and undo. I found it easier to get the baby to sit at the optimum position (so you can kiss the top of their head) in the BB compared with some others which seemed to sit quite low down or far too high even with professionals helping us to adjust, and he enjoyed being in it. We once did back carry on the ergo and it chaffed his thighs so badly we had to take him to the dr, despite using a sling library to ensure we had him in it correctly. I think a lot of it depends on your body shape, I had a big chest and baby belly and the BB works well for my shape and was the only one my husband got on well with too. Also I know a lot of people don't agree with front facing carry (because of the less ergonomic leg hang) but my son absolutely loved it and I carried him front facing for a few months and it was often the only thing that cured tantrums. This carrier allows you the flexibility to carry inwards, front facing or back carry. Despite many people not agreeing with front facing, our relatives consultant said it actually doesn't do any damage if it's for a short period of time, eg for the occasional visit to a farm which is what we used it for, then turned him round again once there was nothing for him to look at.
Another thing worth investigating now, which I still haven't nailed, is some kind of bag to use with the sling/carrier. You'll need both hands so won't want a bag that you carry with your hands but it's cumbersome carrying a rucksack on your back and a baby on your front, and impossible if you're doing back carry later on. That's the one area BB fails, I bought an ergo specifically because it has a little pocket which was really helpful for quick trips out but I still needed somewhere to store bottles/toys etc. A standard changing bag that has a shoulder strap could be a bit of a pain.