The ERGO, hands down. Stay away from the Infantino sling, it's been recalled after three infant deaths were reported:
I've had several types of carriers - the Baby Bjorn Active (OK until baby hit 20lbs, very hot in summer), the Baby Bjorn Air (cool for summer but no back support and too expensive), the Infantino sling (recently recalled because of danger of suffocation), the Infantino hip carrier from Target (ouch..) and, after all these failed to ease my back pain, I discovered my all-time favorite Ergo.
The Ergo allowed me to carry my baby for hours at a time very comfortably, let him nap and nurse in privacy. Can't say enough good things about it, I used it while doing housework, running errands, grocery shopping, and while traveling, far more than my stroller actually.
Another great thing about it is that it can be easily adapted for use with any body type - your hubby won't be embarassed to use it either!
I bought mine years ago when it was popular mostly among hikers but now it's become very mainstream. Buy Buy Baby sells a wide assortment of colors and inserts for use with newborns - 5 month olds. Amazon also sells both, with free shipping.
Jetwithkids.com highly recommends the Ergo:
http://www.jetwithkids.com/blog/traveling-with-kids-ergob... (full review)
http://www.jetwithkids.com/faqs.html#bringstroller (use with multiple kids)
"Q / What carrier holds heavier kids?
A/ A great carrier for carrying heavier kids is the ERGObaby In fact, it's great for infants too! I was able to carry my 30 lb. preschooler around London and Vienna without back strain! The carrier is rated to 40lbs., yet
can be folded up and stored in luggage or the bottom of a stroller.
Q/ What makes your recommended carrier so great?
A/ When my child sits in the ERGObaby carrier, his legs are at a 90 degree angle - this is the most comfortable position for the child and best for his little body for long periods (not being suspended by the crotch is a good thing!) When my son fell asleep, his head did not drop back and roll around. Instead the hood was supportive and kept the sun out of his eyes. On cold days, this hood was a wind blocker. Easy to apply, or remove and tuck away, the hood is a great feature of the ERGObaby carrier! "