Hi Jennifer,
I think you will find that both BBB locations are excellent and you will be thrilled with either location. There are a couple of things to think about when making your decision.
If you book at the BBB in Cinderella Castle, theme park admission is required. There is no admission requirement at the DTD location which makes it more accessible.
Little girls love walking around the Magic Kingdom all dressed up as a princess. If you book at the Cinderella Castle location, you may want to bring in a change of clothes for later in the day. Those little dresses are gorgeous but can get really hot and scratchy if you are traveling in the summer months and don't really keep you warm during the cooler months. Even if your daughter insists on wearing the dress all day, I would strongly suggest comfortable shoes. Princess shoes are adorable but weren't made for walking around theme parks all day. It is miserable trying to walk around all day (and the following days) with blisters on your feet.
If you book at the DTD location, your little princess can still walk around with her princess dress on but it probably won't be for as long as she would at BBB in MK so you wouldn't have to bring a change of clothes.
You can see pictures of the inside of both locations at
www.allears.net. Just search for Bibbidi Bobbidi Boutique one their website.
You can make reservations for either
Bibbidi Bobbidi Boutique location by calling 407-939-7895. Reservations are strongly recommended and book up fast.
My vote is for the BBB at Cinderella Castle. There is just something extra magical about being transformed into a princess inside a real castle.
Wishing you magical memories :-)