Id go with the 200g personally, myself. I like the depth of a tank that goes back 36". That is the deciding factor, if I were to choose a tank. Though, if you are a huge fan of tangs, you may want to go with the 72" tank, to give them more length to zoom up and down.
I currently have a 24x24x24 60g cube, which I thought went back nice and deep. I also have a 60x36x24 190g tank, and youd really be amazed how much that extra 12" back really does for the tank's aquascape possibilities. Its the perfect sized tank for me IMO, Id just make it 4-10" taller if I could do it over.
Also, if you go with a 48" tank, rather than 72" tank, you can get away with running (2) halides with a good reflector, rather than the 3 you would need for the 72" tank.
The 200 gets my vote.