I had both for a brief period of time. The Ergo seemed rather bulky for me. I am only 5' 4", so I imagine it would be ok if I were taller.
I like that my Beco has a built-in infant insert. Lots of people here don't use them, but I do. While the Ergo appears cheaper, when you factor in this cost, they are about the same.
I also like that mine has the panel between you and the baby. Many people can't stand this, but I found it is easier to get a little one into a back carry by yourself when the kid is somewhat surrounded by a pouch. Not all Beco's have this, so you have to figure out which generation to get if you want/don't want it.
My biggest complaint about my beco - The tabs that connect the front part of the carrier to the shoulder straps are very heavy duty, but I find them difficult to open and close. This is usually how I get my kid out of it. I also don't think the back clip is easy to do with a front carry. I usually put it on over my head already clipped, but again, not terribly user friendly. The carrier itself is bulky - doesn't easily fit in a diaper bag - but this is no different (any still probably better) than an Ergo.