OK, I own and love my Ergo, but recently tried the Beco Gemini.
Honestly, I love them both for different reasons.
I do find the Ergo a little less fussy with the straps - the Gemini straps criss-cross in back and the clips have another button to release them that the Ergo doesn't have.
If you are narrower in the shoulder, you might do better with a Gemini over an Ergo. I am broad-shouldered and, overall, a fairly "big" person, so the Ergo is proportionate to my frame. But I know someone who'd be a great candidate for the Gemini and she is narrower and a little more "slight" than I am, despite the two of us being about the same height.
My babywearing group leader calls the Gemini a "gateway carrier" - a great carrier to learn about babywearing with - and I'd have to agree. =)
If it had been out when I was doing my research, I might have registered for the Gemini AND the Ergo AND a wrap carrier, as I got the Ergo with DH in mind, but you won't go wrong with either one!
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Liz
DD (3/2010)
"Make mistakes! Get messy!" - Miss Frizzle