I would like to participate in the poll, but I don't know what to answer.
I've been using mostly Safari on my iMac for no other reason than just because, but lately I've had Flock running for sites such as Facebook and Twitter. On my Ubuntu netbook I use either Chrome or Firefox but mostly Chrome since it's lighter than Firefox and my netbook only has 1GB of RAM. I use Chrome on my Ubuntu laptop because it's old and only has 512MB of RAM -- half of what is stated as being required. My office computer -- also running Ubuntu -- runs Firefox mostly for the same reason as above -- just because.
(I know that's a lot of Linux, but MacOS isn't possible due to financial -- and in the case of my office computer bureaucratic -- reasons and Linux is preferable to Windows.)
The browser I like the most, however, is Opera. Unfortunately, there are too many sites that don't work well with it, so I have stopped using it. If those sites worked on or supported Opera, I would probably use it exclusively.
I haven't personally noted any speed differences or problems between browsers. They all seem to work fast enough for me, and I have better things to do than use a stopwatch while I'm browsing.