I had a baby that needed to be worn. A lot. And I owned a LOT of different carriers, and I loved them for different reasons at different times. These were my favorites:
The Moby Wrap is the colicky baby lifesaver. This is a local Chico company, which made them widely available to me when I was living there with my newborn. There is a learning curve for use, but once you get it, wearing your baby with a Moby is really simple. I found that this was the best thing for long-term infant holding, walks, soothing, etc., but was not a great choice for a quick trip into the grocery store. I also didn't care for it in hot weather, when all the fabric is too insulating, and for older kids who want a lot of ups and downs, I preferred mei tai style carriers (I'm counting the Ergo in that category).
This is the Ball Baby Overall Mei Tai carrier. The wide, long straps make this a really comfy carrier for both front and back holds. A lot of mei tais have narrower straps, which can dig in to your shoulders over time. Also the fabric choices are really pretty. Personally I love this carrier more than the Ergo (below), but I think the Ergo may be more practical because you can get a screaming child in and soothed more quickly, and you're more likely to get dad to wear it.
This is the Ergo. This thing saved my life. It's not at all dorky looking, which makes it guy-friendly, it's incredibly easy to put on/put baby in, even in back holds, so you don't have to be an experienced hippie to use it, and it's comfy. The only downside of the Ergo versus Overall Mei Tai is that I found it near impossible to nurse in. This was the carrier I used for the longest period of time, although had I gotten the Ball Baby carrier first, that may not have been the case.
This is an Ellaroo ring sling. Ring slings are a baby wearing category wear you'll really find a lot of variety insofar as prints, etc., if you shop around. I like ring slings for newborns (when they're small enough that having the weight distributed over both shoulders isn't such a big deal). I especially like them (over wrap carriers for young infants) for quick trips. Also, they're the best nursing-carrier, both because of positioning, and because of the fact that the extra fabric makes a great cover for a little privacy.