The 'speed' can be influenced by many different things, and can apply to several different concepts, making it hard to give a definitive answer. However, here are a few things that can denote speed:
* The amount of time it takes the browser to load from the time you click the launch button. They are all close, so there isn't that much of a difference, but there is one. This is usually influenced by the number of processes required to load, how much it takes up in the way of system resources, etc.
* The 'engine' used to load the pages can have an inpact on the amount of time it takes for a page to load. For instance, Internet Explorer used Trident, Firefox and Netscape use Gecko, Opera uses Presto, and Safari uses WebCore. Engines are basically the software that imports information from the internet and displays the formatted information on the screen. I feel Gecko is the best here, but each test can have different results based on numerous other factors. When you combine that with the ever slight difference they make and the various strengths/weaknesses of all involved, it's impossible to have a clear winner.
* The caching ability is second-biggest factor. Caching is the storing of websites on your computer, preferably in RAM, not on the slower hard drive, so that if you go back to the website again in the near future the browser will only have to load a few select items, making the page load much faster. Here Firefox usually comes out the winner, but Opera and Safari win their share of tests too.
* And finally, the major influence is your computer's specs and internet speed. If you have an older computer with limited RAM or a slower processor, the browser is going to take longer to load. If you lack enough RAM, caching will not work well, if at all, meaning the benefits of having such capabilities is nullified. And, of course, a dial-up internet connection is going to take longer to load the content on cnn.com than if you have a cable service.
In summary, there are a lot (way more than what I listed) things that affect 'speed,' which can refer to the length of time it takes the brower to launchd or the amount of time it takes for any given website to be fully loaded. And don't forget that a lot more goes into choosing a browser than just raw speed...look for a comfortable level of stability, security, third-party support, functionality, level to which it can be customized, and layout. If you have any other questions, feel free to come on over to the Browsers forum...we'll be there.
Hope this helps,