Pros: Comfortable for parents and baby, hood for sleeping, easy to adjust
Cons: infant insert works but is awkward and hot, can't face outward
We tried several carriers and the Ergo baby was the only one that really was comfortable for both me and my husband and our daughter too. She is 21 months now, and we still find the Ergo indispensable at times.
She didn't like to be swaddled as an infant, so slings and wraps that impeded free movement of her limbs didn't work at all. There were times when she really wanted to face outward, and we had a cheap infantino carrier a friend got at a yard sale which we would use for those times, but it was very uncomfortable for me and bad for baby's spine to be carried that way too much. We used the infant insert (the heart-2-heart insert) until she was about 4 months old, and it worked well for her in that she seemed comfortable, but it was a little awkward to get her into the carrier, and luckily she grew out of it before it got too hot because it is a big pillowy quilt-like thing that looks really hot.
The hood is the most useful aspect of this carrier. It makes a nice dark little sleeping cocoon and supports the baby's head well when sleeping. DD still will nap well in the Ergo even at 21 months. At various times in her first year it was the only way to get her to take a nap (of any decent length) at all! If she won't or can't nurse to sleep, a walk in the Ergo with the hood up is our trusty back-up solution.
My husband and I share care for DD, so we're constantly having to re-adjust the carrier if the other one has used it last, and the Ergo is easy to adjust to fit different waist and heights. We used it front carry for the first 10 months of so and since then almost exclusively back carry. I tried hip carry once and it worked o.k., but didn't seem worth the effort to switch around the buckles and straps.
I've heard that Boba is now making a carrier that can be used for an infant without a separate insert, and everything I've heard about the Boba suggests that it is very similar to the Ergo. So if I were making the purchase again today, I might consider the Boba instead if I didn't want to use a wrap or sling for the first few months.