I voted for Gunn. The other day, somebody mentioned Gunn and Buffy as a good couple, which I had never thought of before, but it does seem ideal. They both have a maturity beyond their years, both skilled vampire hunters, both have ways of thinking outside the box. Both have suffered, but haven't let it harden them (a problem I see with Robin Wood).
Since Buffy has always been depicted as heterosexual (outside of the comics), I chose a man. But let's face it, Tara would be everyone's perfect girlfriend!