I nannied for years for a family that had multiple carriers and wraps and the Ergo was by far my favorite. It was the only one I found easy to use AND comfortable for carrying bigger children. So many carriers, slings, and wraps would give me shoulder or back pain after hours of use, but never the Ergo. I've worn my daughter in it on extensive hikes and it distributes her weight evenly to my hips.
I don't think the Ergo is ideal for newborns, even with the infant insert. However, from age 5months and older, its my go-to carrier. If I could change one thing, I'd re-position the pocket so that the zipper was on the top, rather than the side (my keys always fall on the ground when I open it) and make it slightly bigger so that I could easily fit keys, cellphone, and snack inside.