Ranked in these QuestionsQuestion Ranking
Pro Automatically determines the best timer
Benchmark.js has a number of timers available for different platforms and will chose whichever one is the highest resolution for your specific platform. This lets you know you're getting the most precise measurements, regardless of what you're developing on.
Pro Simple syntax
Benchmark.js takes most of the fiddling out of typical benchmarking. As an example, most benchmarkers will need you to specify the number of times you want a function tested, but benchmark.js handles the iterations for you. All you need to do is write the test.
Con Simple syntax can mean less control
Benchmark.js calls really simply, which is great, but it can lead to having less control over a specific test.