A carrier that distributes the baby's weight on both shoulders...that was the ticket for me with my babies...especially middle guy who was just huge and heavy.
For comfort wearing my favorite was my Kozy (mei tai) wrap. I loved that it was all cloth, no buckles. And I could start using it pretty much immediately. My 3rd baby started riding in the Kozy at about 3 weeks old (with legs frogged up.)
For ease of getting baby on my back without additional adult assistance my fave was the Ergo. But I didn't find the Ergo as comfortable, overall, as the Kozy.
So for baby number 3 I had:
~ homemade ring slings (one cotton, one solarveil)
~ homemade moby wrap
~ custom made Kozy
And they each had different uses. But if I could have only gotten one, it would have been the Kozy.