Dreams/Sierra is apparently the most popular, probably because its view rooms are either "pool view' or "DTD view". The rooms facing the courtyard and other towers are "pool view" (as are those in the other towers), and the outward facing rooms have a view of DTD.
Magic Tower has the front desk, lobby and shops, and is closest to the hotel parking lot. I think the restaurants and TV viewing room (near Goofy's Kitchen) are also part of this building, as well as the coffee shop. I think outward facing rooms are considered "city view".
Wonder/Bonita rooms facing the courtyard may have a nice view of the waterfall. Some people love the fact that the sound of the waterfall drowns out the noise from the courtyard/pool/bar. I think outward facing rooms are considered "city view".
I believe I read that concierge rooms are only in Dreams/Sierra Tower.