I would say I'm versatile.
I think its really true though that based on our personality, or mentality in general, that is how we come to the preference of being a top or bottom.
However...as soon as a couple see how big each of them are, I think the smaller one realizes they will be the bottom, and the bigger guy takes control.
Personally, I get really turned on by the bigger guys bottoming. Just the thought that this huge guy wants to be sucked and fucked, maybe more than he wants to take control is a turn on. This huge guy basically becomes my toy... that turns me on just thinking about it.
I dont think there are many relationships though where things are not changed around. I think there is always a usual, but I think people change it up, which is good. You dont want to be the top 100% of the time, you want to give your partner a chance.