I use both regularly however in both very different ways.
For my netbook I use Chrome since rendering space is a premium and Chrome provides the largest view of a website out of IE, FF and Chrome. Also since it's really fast, it runs perfectly fine on my netbook.
For my desktop though, I use Firefox. Reason being that screensize and computer speed isn't an issue on my desktop, I have Firefox setup just the way I like it with themes, extensions, bookmarks and saved usernames and that I prefer having the close tab button below the address bar. Having the tab's IN the title bar doesn't appeal to me at all.
Yes, I know that Chrome would be faster, that it has themes, that I could just transfer my bookmarks, that it now has extensions but the tabs thing is what kills it for me. That and the fact I've been using it since 2005.