Beardies are great lizards, I have a male and a female. They're really tame animals, but if you're a busy person, keep in mind they need daily maintenance. Cleaning feeding etc takes time. If you have the time, go for the dragon.
If you want lower maintenance, go for the BP, feeding is just once weekly, and it's easier to store frozen mice than livefood.
Gallon sizes don't really say much, I like to keep as a rule, 20 sq/in floor space for one or 2 beardies. My new tank will be 3ftx2ft and 2 ft high. I should be getting a BP soon too, but it will be housed in a similar enclosure with the exact same sizes (bit overkill maybe).
JamieLawrence has dragons and was going to take a BP too, but he hasn't been online for a while so I don't know if he has one already.