I downloaded the newest Beta versions of three popular OS X browsers: Opera, Safari and Firefox. To see which one has the best performance, I ran some benchmarks. Here are the results. They pretty much single one browser out as the best.

Acid 3 Rendering Test (longer is better, 100 is max.)

Google V8 Performance Benchmark (longer is better)

SunSpider JavaScript Benchmark (shorter is better)

All tests performed 3 times and averaged, in a clean user-space on Mac OS X using a “typical” MacBook (2.4GHz 2 Duo, 2GB RAM).