It depends. Most of it is personal preference and your budget.
Glass is heavier then Acrylic.
Glass will not scratch as easily as Acrylic. There is scratch removers for acrylic though.
Acrylic will not "tint" the tank like a standard Glass tank.
Acrylic is more resistant to breaking and has more "flex".
Glass has to be sealed with silicone which may leak.
Acrylic is chemically bonded for a permanent seal when done properly (installation must be done properly too).
Here is a LINK with more details on comparing, not just scratching.
In the long run, you will get scratches on both. While Glass is harder to scratch, it will happen at some point.
The cost is a big factor too. I know the link gave a difference but here is a few examples. Notice the larger the tank gets the bigger the price difference. A 300G Acrylic is only ~$300 less then a 500G. If you are looking for an odd custom design, Acrylic is probably what you are going to be looking for, for now anyways.
10 Gal. 20 x 10 x 13 $58
10 Tall 16 x 8 x 17 Tall $34
29 Gal. 30 x 12½ x 17 (Blk Aq Frame Inc.) $105
29 tall 30 x 12½ x 17 Tall $54
100 Long 72 x 18 x 17 (Blk Aq Frame /w Crossbar Inc.) $532
100 Long 72 x 18 x 17 Tall $307
300 Wide 96 x 30 x 24 (Clear Eurobracing) $2063
500 - 8 Wide 96 x 48 x 25 Tall $2310
My husband loves his acrylic tank (26 gallon). I love my glass tanks (30 and 46 gallon).
The only problem he has with the acrylic is that because the tank is one molded piece, the top of the tank offers you much smaller space to fit in decor. He bought this great piece of driftwood that would've looked great in the tank, but couldn't get it through the small opening. Same with other decor he chose. And it wasn't huge decor. It's just the way they mold the tanks.
Know you were asking about scratches, but hope this info comes in handy, too.
Mine is an acrylic 30g long. he above-pposter is correct - the top is molded, so there is little area to insert decor. The really big piece don't go in. The sides bulge out quite a bit, to the point that it is noticeable, but that's kind of the point, right, with the flexing. So far, no scratches on mine, but it is inevitable. Overall, I am satisfied. We went with acrylic because we didn't want the little kids to break it. It was waaaayyy more expensive than glass would have been.