In terms of GUI, Windows DNS is unparalleled. It's simple, clear, straightforward, and easy. I use it for my internal DNS without reservation.
I would think long and hard before I used it externally as the authoritative DNS for my external domain, though. Windows' security history makes me hesitant to trust a server out on the net, even though plenty of people do it every day and don't get their servers cracked. It's probably my relative unfamiliarity with the OS that leads me to this prejudice.
But if GUI is your only concern, there's nothing I've seen easier than Windows DNS server.