My son is a chunker, 22 lb at 6 months, so I needed a really supportive carrier. I have a small frame and even with the Ergo straps tightened all the way, it was not snug enough.
The Oh Snap has a longer body, and better padding and shaping in the hips, with straps there to adjust the way it sits. The sternum strap slides over most of the shoulder strap for perfect placement. It does slide off the end and my husband always manages to do that. To tighten the shoulder straps, you reach under your arms, which make it much easier to tighten with the baby on your back.
Babyhawk makes their carriers in a huge variety of fabrics and lets you pick your design. I have washed it several times and it looks like new.
I can comfortably walk a mile, 7 months pregnant, with my 28 lb two year old on my back in this carrier.