Hmm. my mom always wanted a male dog. I think she was raised with them and found them more protective or smarter- I have no idea. it wouldn't have made a diference to me on way or the other, but I chose Cody out of the litter. He was nuetered at 6months, but never ever marked in the house. In fact it took him a while to lift his leg, and not very high at that. But he did love to mark while walking, seemed like every other step. Since I got him so young, he was affectionate and cuddly and loved to get and give kisses. He was a fast learner too.
When I chose Logan at the SPCA, my mother cringed because she was female. I still never understood what went through her mind. Anyway, although their personalities are so different, Logan is as smart as a whip too, easy to train and a fast learner. She never ever wakes me in the middle of the night to pee. She may only go 2-3 times a day. She never ever gives kisses but loves getting them. Both dogs are (were) protective. My problem with Cody was unsocialization, (my fault), but now I take Logan everywhere. She's still a bit scared at first but warms up nicely.
So, sorry to ramble, but except for the 3am pee outings, I have no preference. I just never met a dog I didn't love. When I ever get another, it'll be by personality. not gender. But since I'm outnumbered by male humans in the house, I may just get a female to even things out!