Try looking for one that is next to the glass watching everything, personally I think that if you get one of those ones, it will be more social to humans. I could be wrong though. Also, the baby's are harder to take care of, so if you want something a little easier, try getting one of the older ones in the cage. Also, if they're bigger, they have a better chance of survival.
I agree with everything above. It's important to have your enclosure ready to go. Pay close attention to lighting (temperatures, light distances, UVB light type and distance, etc). If you have any questions about your setup please let us know and we'll be glad to help you make everything just right for your new buddy. Choosing an active/alert dragon is also a good idea. I've found that more often than not you'll see one that you connect with and that will be your buddy. You'll just know.