we have the Beco Butterfly. I didnt like the looks of the Ergo, and also didnt like that you needed the extra insert for the newborn.
I liked the idea of the Boba, but a) heard lots of people saying it dug in under their arms and b) there was nowhere I could try before I bought it, so that kinda swayed me away.
I tried the Beco Gemini and the Butterfly on in the store, and the Butterfly just seemed nicer - it was thinner material on the body of it, which I liked so it wouldnt' be as hot. And I didnt think we'd use the extra carries the Gemini offered (hip and front facing out) enough. Sooo the Butterfly it was! Love it!