we all remember the 3dmark fiasco with some graphic card constructor did some fiddling to alter their score.
what about javascript engine, or rendering engine ?
of course people in the industry have been known for their fairness and good practice ( especially whose with closed code ).
Again it's a matter of personnal taste,
chrome beta can be extended with some pain, but is fast and could restore most of its memory thank to the whole process separation.
safari is mostly for mac user and eye candy lover, but fast.
opera have very little extension means, is fast enough, and got a lot of feature which cause it to vomit option dialog on your screen
firefox extension make make it grind to a stop but are legions, and make your own browsing experience.
still my choices are opera and firefox.