From what I've read on The Babywearer, the Moby is a pretty good sling for its price, especially for little babies. Depending on how long you intend to wear your child, there are better alternatives if you only want to buy one thing. So if you're mostly looking for something for the first few months, and you like the idea of putting it on and keeping it on for a chunk of time while you pop the baby in and out as needed, the Moby may suit you. Other carriers may be better if you want something you can put on quickly and take off anytime the baby isn't in it. I've got Mei Tais, pouches, and ring slings (some purchased, most I sewed) from when DS2 was little, and the one thing I don't have is a stretchy wrap. I'm going to get one of the
Wrapsody stretchy wraps, which is similar to Moby but a little less stretchy and therefore better for heavier babies. (It's also more expensive.
If you do any wrap research, they were called Gypsy Mama until recently.)
If you want to get only one carrier to last as long as possible, I'd go for a Maya Wrap Lightly Padded Ring Sling (different style from the original Maya Wrap) or a Mei Tai. I can still wear my 2.5 year old in my Maya Wrap or a Mei Tai (though these days I don't wear him much because 33 weeks pregnant is enough added weight). If I could only have 1 carrier to get me from infancy through toddlerhood, I'd get a Mei Tai.