Each browser has its strengths and weaknesses.

IE: Great for corporate use because of GPO support. It has the best support of any browser. It has OS integration. It also has a great programming control that allows it to be more simply integrated into other products. Steam is a perfect example of such a product. On the negative, it is slow, standards resistant, and heavily targeted for exploits. An IE crash usually means you need a reboot. A full blown IE crash could go as far as to mean that you need a full reinstall of Windows itself.

Firefox: It has extensions, which make it great for a daily browser. It is capable of being run in a selective space such as on a thumb drive. It cannot currently have its windows placed as separate processes. It has the most potential to fit a need. It is mostly standards compliant. It is a bitch to work with in corporate environments since they put all of their settings in text files, but those files can be worked on and even directed to point to a network config, so it does function.

Chrome: It is blazingly fast. Each window can be run as an independent process. It has great memory management. JavaScript can be used almost like a compiled programming language with it. Its settings controls are poorly laid out. It doesn't use a standard Window, so it doesn't always play nice. It doesn't always render pages the way you want even though it is very standards compliant (I think this is because of how it renders input control objects). Updates aren't always well tested before they are released.

Opera: Standards compliant to the max. Otherwise it is just a pain in the ass over in the corner. It is fast, and renders well, but it always will be that "other browser" that gets no respect because of its history as a pay product.

Safari: It should be everything that Chrome is, but it isn't. It fucking sucks balls and shouldn't be used. Yes it is fast. Yes it renders most pages well. Yes it never seems to do exactly what it is supposed to. It is the quirkiest browser I have ever used. I am confident when I say that this is my least favorite browser on both the PC and the Mac. However, I am appreciative of it on the iPhone. I honestly wish that Apple would put as much effort into their desktop software as they do into their phone and OS... or just let another company make the damn browsers.