I don't want my kids to have a soulless Mommy, so I can only really think about the boy/girl situation from Wendy's perspective. (To remind-she is the ultimate ruler of creation, and all that is must be pleasurable in her sight. Love her and despair.)
I have a sister, so I know what kind of good and evil that can be. I am also the oldest, and I always thought that an older brother would be much more useful than a younger brother-you know, for kicking peoples asses for you, and being intimidating to boyfriends and stuff. I didn't grow up with a brother of either variety, so I actually know zilch about brothers.
Anyway, it turns out that you can't plan these things, and it doesn't matter what you think.
One of each will be cool.
I'm not exactly sure what to do with a boy, except to put him in geeky sweater vests and tiny bow ties. And possibly name him something that will get him beat up a lot. Poor child.