Many mummies recommend Baby Bjorn. I have seen babies as young as around 2mth old (judging from their size) using it.
For dear son, I actually bought a MIM sling but i dont really know how to use. I started using those mei tai carrier when he was 4mth+ onwards. Cause is more convenient and easy to use for me. But of course, usually we only use it for short trip, like when we're going out to run some errands, usually within 1-2 hours. We used that until dear son was around 9 month old and we bought a Manduca baby carrier. It can be used from 3mth old onwards.
I can tell you Manduca is very worth buying. We feel no stress on the our shoulder. After 1yo, can use to 'piggy-back' the child.
Before you decide on any carrier, always bring along your baby to the retail shop to try it out.