I love my Butterfly. I also have the other two listed by pootlebug 
The butterfly does have some features that are better than the Manduca though (If you get the II and not the first model).
Firstly, you can actually have it fully on and adjusted and then put the baby in, because the front panel unclips and flaps down, which makes it easier to put the baby in.
Secondly, it has an inner panel as well, which means that if you're careful you can take it off with the baby in it, so you can pass it to DH to wear for a while with DC still in it. And on occasion I've laid DS down in it when he's been asleep. Whereas with the other two he almost always wakes up if I take them off.
The Manduca is also fab in my opinion. DH tends to wear it more than I do. And it can do a hip carry, although I've not really used that much.
The Connecta was the first one I had. It's very good, but much more basic. I keep it in a pouch in the pram and it's my emergency out and about sling.
When DC2 is born DS will still be well within the weight limits for them, so I'm hoping they'll get much more use when we all go out en famille attempting to justify ridiculous sling ownership