Maple will give a more full and open sound, whereas birch absorbs a bit more sound to give a more focused tone. You can find more info about diffent wood types here
Drum Woods
Personnally I'm planninng to go with maple as I want lots of projection and if I want a more focussed sound later, I can always buy thicker heads.
I too was interested in Mapex, however, I would strongly advise going with either the sonor or even the brand new PDP Platinum Maple. The Mapex just seemed to be a very thin shell and I question how long they'll hold their quality compared to the others.
Good luck and let us know what you get.