I have 2 bECOs and 2 Ergos and if I had to choose, I would definitely choose a bECO. The Ergo is made of sturdy canvas so it's a great workhorse carrier, but that also makes it more bulkier to me.
I love the gorgeous fabrics of the bECO. It's made of a lighterweight fabric, but I love that I can fold it up smaller. It also comes with a stay put strap so you can roll up the body and wear it around your waist without any dangling straps hanging down.
As far as comfort, I prefer the bECO to the Ergo. I think the Ergo feels a little too bulky for me. I also feel like I'm going to go backpacking. I'm petite and thin so that might have something to do with it.
The Ergo does have that nifty zippered pocket which can come in handy.
I do think they are both great carriers which is why I have 2 of each.