I think if you're male, sexually/romantically (whatever, you get what I mean) you should be with a female. If you're female, well duh, be with a male. I mean, that's why there are two genders in the human race! One gender is supposed to go with the opposite in that kind of relationship.
Personally I'm repulsed by the idea of being attracted to someone of my own gender. If someone suggests it, I'll be like "eugh..."
Did you notice that with gay couples, one of the guys is kinda feminine and with lesbian couples, one of the girls is kinda masculine? Then what the heck, go for a REAL female or a REAL male. Sometimes people are plain weird...