Depends on your use case and programming language you feel convenient. Fo example:
Flask is great if you like python: http://flask.pocoo.org/
If you are more on the Java side you might give Spark a shot: http://sparkjava.com/
Best for what? A hammer and a screwdriver are both the best tool, but not for the same job.
As a language its falling out of favor I think, but there's nothing simpler than Sinatra in Ruby