The only benefits of glass is that it's clearer, and it will not stain or scratch as easily, and is compatible with every coolant commercially available.
Benefits of PETG are that it's really easy to work with, is more forgiving, is able to be bent (saving money on fittings) and is cheaper.
Acrylic is cheaper yet and slightly more compatible with coolants than PETG, but can be brittle (not REALLY a big deal in a case) and is slightly more difficult to bend than PETG. It is also more clear than PETG, but not as clear as glass.