Out of the ones you named, I've only used an Ergo. Since, I've upgraded to both a Tula and a Kinderpack and both are a million, billion times more comfortable than the Ergo :
I have both an Ergo and a Butterfly 2. I got the Ergo when my older girls were about a year old and love it. I've used it mainly for back carries. I got a Butterfly 2 for this LO because from what I can tell it is better for infants (and it was on mamabargains :-). I like that it's a structured carrier like the Ergo and therefore pretty easy to put on. The Butterfly is different in that you actually "strap" the baby in the carrier before you put it on and the infant "insert" is actually an additional strapping in which makes it feel quite secure. I also have a K'tan and I like the Butterfly better when out and about or when I'm trying to get something done because I don't feel like I still need to keep a hand on her.
2004-Started TTC; Nov 2007-Lap with endo removed; Jan 2008-Ectopic (mtx); April 2008-IVF #1 (bfp, twin girls); March 2011-FET (cp); June 2012-IVF #2 (bfp, singleton, EDD 3-19-12)
***Twin fraternal girls born at 35w6d in 12/2008***
Re: carrier type question?
***Twin fraternal girls born at 35w6d in 12/2008***