I've used an Ergo with the infant insert and a K'tan with my newborn. Both worked really well and I would definitely recommend them for the early stage. I liked the k'tan better for carrying him indoors and the ergo better for outdoors/walking longer distances. He's just 7 weeks old, so I'm not sure how I'll like them once he's older.
A few things to think about those carriers: The ergo infant insert has been great to use with a December baby in WI, but it is padded and would probably be very hot to use in warm weather. The K'tan comes sized to fit you, so it's hard to use with more than one person. My husband and I were both using ours and his larger frame stretched it out so now it works really well for him, but doesn't work for me anymore. (I just bought a moby so I have a soft carrier that fits me.)