Waterfox is a 64-bit compile of the latest version of Firefox. The pro is that it's faster. The con is that it doesn't offer anything different from Firefox other than speed.
Pale Moon has both 32- and 64-bit versions and has more customization options. The pro is that you have more options available. The con is that it consumes more resources than Waterfox.
If you want speed, download Waterfox. If you want to customize, download Pale Moon.
Edited by Daikun - 12/21/13 at 7:09pm