sling or front carrier?
I am a big fan of the baby bjorn front carrier. Why? It is well made, easy to use, it isn't too bad on the back,and has a fairly long use life (as far as any baby product goes). They are pricey to buy new, but I found one on ebay.
Our daughter was not quite 8 months old when we used a front carrier at WDW. It was such a blessing for us--much easier to strap Anna on and go than to try to hold her in lines, watching shows, etc. Having her in the carrier put her up higher so she could see the "world"
We also used it at 10 months, which was a bigger challenge. She had discovered crawling and wanted no part of being held back, LOL!