Well, there is no one BEST baby carrier; each one has it's pros and cons, so it depends on what you want to use it for. Slings are great for their versatility, pouches are great for ease of use, mei teis are fabulous for long term comfort and back carries. I have a Kozy (mentioned below) and I adore it - don't know how I could live without it. A sling is somewhat easier to use with a newborn, as are wraparound carriers such as the Hug-a-bub. Are you familiar with this site?
http://www.thebabywearer.com/
There is excellent info on there on different types of carriers and how to choose, as well as reviews on specific carriers.
Since someone else mentioned it, I have to say something about the Baby Bjorn and similar carriers. They way they are designed causes most of the baby's weight to be carried between their legs, and there is some concern that this can cause problems with spinal compression and proper hip development. It's probably not a big deal if you don't plan on using it much, but otherwise it might be an issues.