quick bluesmirf question

on this module: http://www.sparkfun.com/products/158

It says voltage spec: 3.3-6VDC

I've seen schem's with both 3.3 and 5 being used. Is there a correct power voltage, or do either work (which is what i'm assuming)? Is the transmission power higher with the 5V vs 3.3? IE, any pros/cons to each voltage?