I have a 5g acrylic and it's okay but it does scratch easy, and when acrylic ages, it gets brittle and will simply shatter or crumble once it's lost it's strength. It's much, much lighter than glass however and I think removing scratches out of it is pretty easy. A downside is it tends to yellow over time, making the water look discolored.
It's "one piece" unlike glass so it's built into the shape it will be instead of "glued" like glass so the odds of a leak are reduced. It has a few other advantages and disadvantages I can't think of right now.
Glass on the otherhand lasts a lot longer, isn't as easy to scratch but it is harder to remove scratches (almost impossible in some cases). Glass can be more durable to heat, it won't melt like acrylic can at lower temperatures (though this is usually not an issue unless a heater malfunctions) and glass is the mainstay of the aquarium hobby.
Really, it comes down to personal choice. I prefer glass to acrylic.