We have one, and think it's great. My ds is 19 months and 33# already, so carrying him in anything isn't the easiest, but the Ergo is lightweight, easy to pack, well made and seems to distribute the pounds pretty comfortably. We didn't get it until he was already 16 months old, but I plan to use it a lot more with the next baby, when we have one.
I love our ERGO. DS is almost 14 mos. and about 27 lbs. I can carry him comfortable (I'm 5'4" and 110 lbs) and so can SO (he's 6'10" and 270). Looks liek we've still got plenty of growing room in it, so we'll be using it for a while.
I have an Ergo and love it. I don't have much experience with others to compare it too, but we've had ours maybe 3 months and I already feel I've got my money's worth out of it. I use it for both front and back carry.