You might consider the Kid Comfort II if you travel ...
Outstanding construction and adjustability
Too long and bulky. The price may be high for some.
The Kid Comfort Child Carriers (III and II) are the most adjustable and most rugged I found. The only down side of the Kid Comfort III is that it has a built-in sunshade/tall headrest that increases the height and bulk of the carrier. We found that it was too much for car and air travel and we chose to go with the Kid Comfort II.