We've BBBooed at DTD 2x now, and it was very nice. Of course, we didn't have a choice.
Our next appointment is in the castle, because it seems like the perfect place to be a princess.
At DTD it isn't terribly "magical", and you wind up going somewhere else to show off anyway, I can only imagine. However, it's done very well, and if you have time to travel to a second destination afterwards, I can't imagine there is TOO much of a difference.
However, I haven't done the castle yet. Hopefully there will be some folks who have just went and can reply with a more educated answer.
As long as the size of the boutique and staffing is the same as DTD, I can only imagine the Castle would be the natural choice...
Of course that requires park admission tickets, where as DTD does not.
Either way, I'm sure it's be a wonderful time!