I thought the Boy Pig would be boss! Our Oscar is the most laid back out of all of ours, our Boss Piggle is Daisy, she is the largest. I found out for sure as she was mounting one of our "babies" last week when she was in season. All is calm again now, the most obvious trait in our colony is the Under Pig, who is Amber. She is also the Wheekiest! Doesn't stop the others nudging her out of the way for hay etc, but on the whole they do all get on well, and Amber is not bullied.
I think in a group that generally get on well, the dominant pig may not be that obvious. Perhaps you're lucky in that respect!