I really don't have a favorite but I lean more towards Voice Search because it is very accurate.
You can make Voice Search work with the Android keyboard by selecting Settings --> Language & Keyboard --> Android Keyboard --> Voice Input --> On Main Keyboard.
I prefer the Hacker's Keyboard because it integrates Voice Search better across multiple Apps versus the Android keyboard.
I have never tried Flex T9, but it has high reviews on Amazon and is reported as compatible with the Entourage Edge -
http://www.amazon.com/Nuance-Communi...5810226&sr=1-9