Having one carrier from newborn to toddler-age can be tough. I think different carriers are better at different ages.
We used a Moby Wrap with my daughter up to about 3.5 months of age. I like the Moby Wrap best for newborns, as there are many different positions that you can put baby in (some babies like the cradle hold, others like to be more upright). It's also cheap ($35 retail), so if you end up not liking babywearing, you're not out much $$$. It's a little stretchy for older infants/toddlers, though, and you can't easily do back holds in it.
We switched to an Ergo when she was 3.5 months old. The Ergo is not good for newborns -- it requires a special insert, which costs almost as much as the Moby Wrap! But it's great for older babies and toddlers. My daughter is 1 year old and we use it almost daily and plan to continue using it for quite a while. It's also the only carrier that my husband will wear -- he considers the others to be too "girly."
I now have a Hotsling as well. I leave it in the bottom of my diaper bag so that I'm never without a carrier. It is nowhere near as comfortable as the Moby or Ergo for long-term use, but it's great for quick errands.