This one -> [ame="http://www.orbithangar.com/searchid.php?ID=4530"]Burn Time Calculator 2.32[/ame] <- Is the latest version so I'd recommended using that one.
The difference that I've noticed is that one (v.2.32) calculates the Δv from the main fuel tank while the other (v.1.5) calculates it for the main and rcs tanks combined.