Moby Wrap: many people love this one. I tried it and found it to be very comfortable (you can read my full review here). However, I did not end up reaching for it often because I felt like I was sort of drowning in all that fabric. Also, it seemed like once I got the baby all wrapped up and snuggly, she wanted to nurse or needed a diaper change or I had to take her out for some reason.
Ergo: I like wearing the Ergo on my back once baby is a bit older. On my front it feels bulky and I can't bend over or sit while wearing it. (I'm 5'5" and have a small frame.) I didn't care for the infant insert for this reason, I just don't like the Ergo for a front carry around the house. The infant insert also props the baby up higher and into my face a bit much. If I'm out shopping and walking around, the Ergo is fine on my front. I guess I'd call this one my "out and about" carrier.
Mei Tai: I made my own mei tai, similar to a Babyhawk. It worked well for a back carry, but I made the body too large. My babies felt a bit smothered when worn facing my front in the mei tai, they couldn't see out and the ties seemed to squish them. I'm trying a Babyhawk this time around because I think the smaller body will work better.
Ring Sling: I have a Maya Wrap ring sling that I really like wearing newborns in. The upright carrying position is my favorite and seems to work well. The rings on it are super heavy and the tail is long, so I purchased a new ring sling to use with the new baby.
With three other children to chase around, having plenty of baby wearing options is a good thing! To recap: The ring sling is my go-to carrier at first when baby is tiny. Once he/she has a bit of head control I will use the mei tai. The Ergo is great for keeping in the car and using out and about as baby gets older. There are plenty of other carriers out there that I haven't tried, these are just my thoughts on the few that I own. I'll have to post an update after baby arrives and let you know what our new little bundle thinks of the carriers. :)
Do you have a favorite baby carrier?