I had a Moby, Ergo, and Snugli when I had DS1.
The Moby was my favorite for the itty bitty stage. When he became more curious and started leaning all over the place it was time to retire the Moby. T
he Ergo definitely gets an A+ for the older babies IMO. I was able to put him on my chest for hours at a time (went to the zoo with a friend for a few hours) when I was pg with my twins, and while I could feel his weight, it wasn't uncomfortable.
For some reason, I've never been able to wear a baby on my back comfortably.