Baby Slings and Carriers

I saw this girl the other day with a baby in a sling and it kinda looked like her arm was in the sling. After seeing that I'm not sure if baby slings are right for my friends. It just seems that baby carriers are more sturdy and safe....plus those mai tei carriers let you carrier your baby on your back. I'm looking to have some answers as I start going through more sites. If you have links that I can look at, or have suggestions, just post me :)