If you want faster,then definately Waterfox. but if you want more dev options. then Firefox developers version.

in Firefox developers version website page:

https://www.mozilla.org/en-US/firefox/desktop/fast/

mozilla compare Dev version to others, subject is: "Faster than ever"

s.Turjoe are u sure about that? Waterfox even faster than Dev version?

I'm pretty sure because those browsers are comared with 32bit versions of browser. As Waterfox is solely made for 64bit architecture. It could utilize system resources from 64 bit OS more resulting faster performance. I've installed it and saw the process manager on my windows 8.1 64bit machine. which showed it is running on 32 bit. So technically waterfox should give more performance than firefox dev version. -Thank you

Waterfox however is not based on any stable Win64 source from Mozilla as Mozilla will not have stable Win64 Releases until as early as Firefox 37.0 in first phase. Mozilla could build the Win64 Release now just as the Waterfox author does though it would not be stable.