I would go with glass in a smaller tank, but for larger tanks i would probably choose acrylic. For the record, Acrylic lets in 12% more white light in then glass, and glass is about 1.5 times heavier then acrylic. Dont forget that acrylic is also not prone to crack and shatter like glass. But....the 12% in light means nothing when the tank is filled up, you only move you tank once in most cases (besides a little extra weight will help your muscles, and small tanks are not bad empty anyway), and cracking is only bad if you've got drunken friends over or a mantis shrimp (get rid of both and problem solved.)
Bottom line....acrylics selling point is the weight (a factor for larger tanks), and ability to be molded however the heck you want it