that's a bit like asking who is the ultimate rock-n-roll band, except that just so happens to be the Moody Blues (which can be verified independently).
i was a huge FF buff, but lately chrome took top honors. chrome seems to handle the java plug-in more efficiently. also, chrome has the built-in debugger where with FF you have to install firebug.
also, the chrome-php is way cool in that its super-easy to have php dump stuff into the chrome console. yes i know FF has something quite similar, but it seems like the FF one didnt work quite as dependability as the chrome one did.
in the android world, i found FF is better, surprisingly enough.
side-note: recently i was forced to upgrade the internet-explorer, and IE installed four other programs - yes i was not paying attention. four!! that's a total disgrace. fortunately, i purchased the revo-uninstaller to deal with problems like this. but note that chrome has an IE add-on. every time i use IE, i have to wash my hands in bleach to get the stink off.
this is worth looking at too:
http://my-debugbar.com/wiki/IETester/HomePage
since every time IE comes out with a new version, it is incompatible with the last one !
quags - does chrome have something similar with proxy?