I use Chrome as my main browser after switching from FF.
I still use FF as a backup when I wonder if cookies are breaking something or if I need to double check a site layout..
Chrome is faster. (Each tab is running on a separate core of my quad core CPU)
I like the plugins in Chrome more than the plugins in FF (likely because they are all new/working?)
Chrome just works better (more screen space/tabs are way smarter)
Chrome doesn't crash (Tabs will crash but the browser never dies)
Flash works so much better in Chrome, I saw a friend trying to play the same flash video game as me in FF and he had delays of up to 5 seconds for things that were instant for me in Chrome.
Chrome is smarter about it's files/locations with modern OSes
Chrome comes in MANY self-contained versions. I can load GMail in Chromium Iron and then login to a company google account in Chrome without any confusion.
FF doesn't have an entire OS project based around it (Chrome OS is pretty slick!)
FF reminds me of nutscrape agrivator, which I refused to support just because it was the best alternative to IE. I use the best browser, I don't care who made it, but it does suck when I'm reminded of kludge when I am using FF.
Opera is handy because it has the turbo mode which is great for stealthing and slow connections. I also like the spiffy new extended preview tabs, that looks "keen", but don't know I'd "need" it and may not even "want" it after the novelty wears off.
IE is essential to have some experience with, if you have to help someone else out and don't know what browser they have you can always get a website loaded quickly with WinKey+R "iexplore" [ENTER] on any windows PC.
Safari? Gesh, I used it on a mac a couple times. Seemed slow and cluttered. Looked like something Mozilla based, which I don't like.