In most cases, I prefer glass aquariums for a few reasons. For one thing, they don’t scratch as easily. Theoretically, this means they ought to keep looking good as the year's pass. They also tend to be less expensive.
Finally, I trust the construction of a well-made glass aquarium a little more than I do an acrylic tank. This is especially true for large tanks, which may need to hold up over the years without looking dull or, worse, leaking.
However, acrylic does have some advantages. Acrylic tanks are lighter, and they are available in some interesting shapes and configurations that are tough to achieve with glass.
When it comes to small tanks around 5 gallons, I think acrylic options are often a good choice. There are many acrylic aquariums on the market that come with everything you need to start up your tank.
If you are new to fish keeping, or if you don’t want to spend a lot of time hunting down accessories, they’re simply more comfortable to work with than a traditional glass tank.
So, for the person who wants an aquarium 10-gallons or larger which they intend to keep running for years, I recommend considering a glass tank.
For someone who wants a small, attractive, easy-to-deal-with 5-gallon tank for a betta fish (for example) I think acrylic is fine.