There are pros and cons with both. Here is my thoughts on the matter:
Glass
Pros- Scratch resistant, easily available, relatively inexpensive
Cons- Heavy, can not remove scratches, transfers heat worse then acrylic
Acrylic
Pros- Can fix scratches, light, natural insulator, strong
Cons- not as easily available, scratches if you look at it wrong
I think both are great, but I'm lazy and cheap and would just pick up what they have at the LFS or what is available in the classifieds.
Sculpin