I always get the bowl, and I always have left overs. It is so much food. Plus, if you really want a burrito you can get the bowl and ask for a tortilla on the side for no extra charge - best of both worlds!
For the most value, you should get a burrito bowl. http://www.businessinsider.com/popular-secret-menu-items-chipotle-hq-2013-2 The video at the bottom of this article shows that when ordering a burrito vs a burrito bowl (with the same ingredients) customers actually get 70% more food by weight than if they ordered the burrito! Plus you're saving calories/carbs by not eating the tortilla!