I have both. The Ergo is super sturdy, it has a carrying pocket (can fit a diaper, wipes, keys, money, etc.), the seat is nice and wide. The Beco is prettier (more like a MT), much less bulky, is lighter, folds up much smaller (easier to throw in a purse when you're not wearing DC), has a stay-put strap that lets you roll it up into kind of like a fanny pack and keep it on your waist when you're not using it, it feels more comfortable to me than the Ergo if you ever use a front carry. The sleeping hood is about the same on each (one has snaps, one has clips). The Beco is taller, so it comes up higher behind my DD's back--it's harder for a toddler to try to back-dive out of a Beco. My DD likes the Ergo better, I think because of the wide seat (good for toddlers). I like the Beco better, probably because the higher back keeps her more snug against my body. Although, I did find the Ergo more comfortable than the Beco in the winter because it's roomier for when you're wearing jackets (I have a hard time getting the Beco over my DD when she's wearing lots of clothes). I think the Ergo is better constructed, but it is made in China and comes in a vinyl bag that smells of chemicals (the Beco is made locally).
They're both wonderful carriers! You can't go wrong.