I think you like couples that have a strong foundation in friendship where the "shipping" is really blurred between strong bonds of friendship and something more overtly romantic. I think you also like ships that are a little bit unusual - not necessarily star-crossed exactly, but unconventional. John/Aeryn and Doctor/Rose are both alien/human pairings, Guy/Marian were basically on opposite sides of a war, and Ned/Chuck can't touch. I think you also like couples that make each other happy and encourage each other to be better people.