I recommend unreservedly the Baby Bjorn baby sling. It’s fairly simple to use (for me anyway), it keeps the baby at the right height, and distributes the load fairly between your shoulders and waist.
We also have a Tomy sling which at first sight looks more comfortable, being all fleecy and fluffy. However, I find the shoulder straps too long, and I had to take it off to adjust it properly. The Tomy also fails to take into account those of us with…ummm…larger chests. So you get the fasteners jabbing into the side of your already tender breasts, and I’m sure it doesn’t do them any good. I also found that Ceej started slipping down towards the stomach, coming to rest against the roll of flab above my c-section scar. While I still don’t have any stomach muscles, it was quite painful.