if you aren't careful acrylic scratches, but I've had my tank up since novemember and aside from one tiny scratch it came with, nothing. My trick is I never use algae scrapers. I let teh snails keep my glass spotless (olive nerites are great for this).
acrylic is usually more expensive tho, so if you are on a budget I'd go glass. If you aren't on a budget, check out the ada rimless tanks at www.aquaticdesigngroup.com
. They are gorgeous.