acrylic- lighter when empty, wont smash if you drop a rock into it when aquascaping. Scratches very easily, can stress craze over time if poorly heat formed during manufacturing, UV light makes it go yellow over long periods of time. If it does crack it's curtains for the tank.
glass- heavier when empty, wont scratch as easily, broken panes can be easily replaced. Can be resealed and effectively will last forever if looked after.