I have had 3 carriers- a sling, the moby and the ergo
The Sling
Pros- small, easy to fit in a diaper bag, great for newborns, easy to put on
Cons-
I was constantly checking to make sure the baby's chin wasn't touching
his neck. You have to buy the correct size and it is hard to gauge the
correct size when you are pregnant.
I had this one for Trey, but honestly he slept so well in his
car seat that I didn't use it as much as the other ones. I was also the
most worried about how he fit in, but that could be that I was new mom
so everything made me more nervous. I wore it from birth until Trey was
about a year (then I didn't really wear him again because I was already
pregnant!).
Moby Wrap- I had this for baby Charlotte and Esther.
Pros-
Charlotte loved it, most like being in the womb, soft and easy to
wash, I put it on before I go somewhere then when I get to the store I
take the baby out of the carseat and put her in the moby. It has much
more back support than the sling. One size fits all so if you lose
weight after the baby you can just tie it around you tighter and it
still fits. I wore this for walks, going to the library with the baby
and even apple picking when Charlotte was about 10 months old.

Please forgive my exhausted look, this was the baby that didn't sleep :) This is the moby with 2 week old Charlotte. If I needed Charlotte to take a good nap when she was a newborn I put her in the moby.
Esther in the moby at 2 months old. She hated having her head tucked in so I always I had to hold her head.
Cons- For the newborn carry you have to tuck the baby's
head into the fabric so it is truly hands free. Charlotte did not mind
this and liked being tucked in. Esther hated it, even when she was fast
asleep in the moby if I attempted to tuck her head in the fabric she
would wake up and start screaming. Also when you are out there is a ton
of fabric to wrap around you so it is hard to keep it from touching the
floor while wrapping.
Ergo- Love this!! It is by far my favorite carrier of the three. I have only had it for Esther, but I use it all the time.
Pros-
Great back support and easy to put on by yourself. I can see how it
would still be comfortable as baby gets older. My husband is willing
to wear it if necessary (He wouldn't come close to the sling or moby:)
Esther loves it and she is not a fan of the Moby. I feel very
comfortable bending over wearing it as it is truly hands free, where as
the other two carriers I always felt the need to keep one hand on the
baby when I would bend over. It also has a shade that you can pull over
a sleeping baby to keep the head completely covered.
Cons- You have to get the newborn insert to use from
birth-about 3/4 months. About 3 1/2 months I stopped using the newborn
insert for Esther because she had plenty of head control. Trey had
a very floppy neck so I probably would have had to use the insert
longer for him. Most expensive carrier. The insert can be a bit warm,
but if you are wearing baby anytime other than that hot summer months
outside it is fine. Plus if you have a newborn, you usually aren't
outside for extended periods of time anyways. Inside my house or a
store I didn't find the newborn insert too hot.

Esther in the newborn insert.
If
I had to choose just one carrier I would invest in the ergo with the
baby insert. It is the most expensive, but I think it has the most
longevity and is very supportive for the wearer's back and hips. I
thought about the K'tan breeze, but I don't know anyone personally who
has a K'tan, so I was hesitant to buy it since I already have so many
carriers :) Also for help figuring out how to use each carrier there
are tons of you tube videos! Just search for the different carrier in
you tube and watch the videos that demonstrate the different holds. I
found the videos way more helpful than the owners manuals.
I bought my Ergo carrier and newborn insert off
zulilly.com
so I paid half the cost of it. I don't know how often the Ergo is sold
on zulily, probably every few months, but it is worth checking into. I
found the first 2 months of life I wore the baby all the time, even at
home, just because it made my baby's sleep better and it was easier than
sitting on the sofa holding them all day. Once my baby's got out of
the newborn sleeping all the time phase, I mainly use the carrier when I
am out and about. It is so much easier than lugging around the car
seat or having to deal with the stroller every time I get in and out of
the car.