Subjective opinions are nice and all, but two months ago Tom's Hardware did another of their extensive benchmarks of the four major browsers on OSX and Win7, so you can have real numbers (though impression is actually worth something--if it feels faster, it doesn't really matter if it technically isn't):
http://www.tomshardware.com/reviews/macbook-air-chrome-16-firefox-9-benchmark,3108-17.html
All the results are very dependent on the particular thing being done, and you can read through them yourself, but a few general observations:
If we're talking about page load times (on the Mac, of course), for uncached pages Chrome is the fastest, followed by FF, then Safari, with Opera bringing up the rear. For cached pages, Safari is the fastest, followed by Chrome, then FF, with Opera again bringing up the rear. Also interesting that IE on Windows is slower than any other browser on either Mac or Windows.
Safari on the Mac starts up cold (and/or with a single tab) faster than any other browser, while it's the slowest to re-start with several tabs open.
For complex Javascript, the results are all over the place, but for most tests Chrome and FF are close to each other out in front, with Safari a ways behind, and Opera way in the back in all but one test, although all thee of the other browsers were fastest in at least one of the many benchmarks they tried.
If you get into the arcane stuff, for DOM performance FF is fastest, followed by Chrome, Safari, and Opera Mac (although Opera on Windows beat everything else, period). On a complex CSS test, Safari wins followed closely by Chrome, then Opera, and FF is absolutely dog-slow, taking 23 times longer than Safari.
For RAM use, Chrome is way out in front, followed by Opera, then Safari (at around double what Chrome uses), then Firefox (that one definitely backs my real-world experience--Safari is something of a hog, and FF is terrible about memory management on the Mac; the Windows version is drastically better).
Honestly, the only two that matter much for real-world everyday use are probably page load and RAM use, and with the exception of FF and Safari's love of RAM (which may matter if you're on a 2GB system or run a lot of stuff and don't quit things often) there's not really enough difference to make or break any of them--it comes down to taste and which feels faster for what you're doing. Chrome, on average, is the fastest, followed by Safari, then Firefox, and Opera tends to be the slowest.