My DH's favorite is a robozo (he remembered what it was called not me
). Basically, it's a long piece of fabric that you wrap around you and baby and tie however you like.
He likes it because:
It folds up easily to pack.
It fits a baby all the way up to a preschooler hands-free.
He has complete control and can adust it to carry them in what ever position is most comfortable or convienent for what he's going to be doing while carrying them.
If he has a sore or pulled muscle, he can decide where the knot rests so it doesn't press against something tender making it irritated, or adjust it to dstribute the weight accordingly. He also like having it knot somewhere other than his shoulder if he's going to carry his laptop case or a diaper bag.
Legs can be tucked in or left free. [And he'll tuck the toddler's legs in if he's going to be cooking or using tools and doesn't want to risk a stray limb appearing in his way and into a dangerous situation but doesn't want to tell him to just go stay with mom for awhile.]
He can wear them tight and snugly against him or leave it a bit looser to allow them freedom of movement or ease of in and out (for the boys who may change their minds about walking).
He also loves the simplicity of it, he says it made he realize that in a pinch he could just grab a sturdy bedsheet and make do. He'd also like a longer one because he thinks with more length he could figure out ways to carry two at once without using two of them.
He'll also use the backpack/frontpack carrier with the baby but doesn't prefer it. I'm not crazy about the robozo because I don't find it easy enough to suit me, but honestly he carries them more. And when I carry one of the boys I tend to throw them on my back and make them hold on and I'll use the little infant frontpack/backpack carrier we were gifted when I had DS1 with DD (she's still the size of a 4 or 5 mo old)--well not lately since I left it at my grandmother's house in MS. I'd really like a pouch or hip carrier to use on the boys but no funds to get one... I know it's not adustable but I'd love the ease of put it on and go. I imagine it depends a lot on what you want out of a carrier...my hubby likes adaptability it seems.