I checked Google Word for "best in town" and it looks like this phrase is commonly used for food and eateries.
Both foods and eateries belong to a class of things that can be found only in some geographical location, hence the phrase 'in town'.
I wonder if this phrase can be applied to something that can't be pinpointed to a particular physical location.
For example, could I say something like:
Check out those five websites. You won't regret it. They are best in town!