I LOVE my ring sling by Sleeping Baby Productions. I actually just ordered a second one in another color and fabric. I have a Tencel fabric one now, and it is very soft, light, and breathable, but strong. Perfect for summer. I've been wearing my baby (almost 4 weeks old) in it every day. I just ordered a twill fabric one in black, though I wish she had the Tencel fabric in black. She gets new fabrics all the time, though, so you just have to keep checking. The shoulders are GREAT and really distribute the baby's weight well. I've had no back pain at all. There is a learning curve if you've never used a sling before, but ring slings are much easier than the Moby wrap IMO. Here's the link:
I also have a Moby wrap, but it's more complicated to get the baby in and out, so I haven't really used it yet. I think I will use it more when the baby gets a little heavier and I need to distribute the weight on both shoulders and/or I will be carrying the baby for a long time. We're planning to get a Beco Gemini soft structured carrier soon too, for longer outings and travel.