Another one with a DS (3) and a DD (5).
I really love the mother daughter connection I have DD, and I enjoy the intensity of our relationship - she is very focussed and loves it when we plan something fun together - she gets such a kick out of 'special' times together...and she is very intense, also very affectionate, very intelligent, very bossy and can be cheeky and manipulative. I adore her, but I wouldn't stay I find her easy to deal with...its a constant negotiation with her.
DS is far less intense, more easy going, happy to just be, to chat, to play. He has a wonderful sense of humour and is cheeky in a rascally way, not a defiant way. When he is angry, he snaps into physical agression, and I find that hard to deal with, though not as hard as DD's rudeness.
To be honest, I probably enjoy DS more often, but DD more intensly. They both have their challenges and their joys.
I think personality is a much bigger factor, and I think birth order can greatly influence personality - it seems to have done so with my two anway.