They're both pretty similar because they could overlap and I'd defnitely advise you mention both, but if I had to choose one it'd be gender because there's more theorists (tannen, lackoff etc), you can use common sense to comment on things like over lapping, women tend to talk more etc if you get stuck and it's alot more obvious to pick out in texts. But even if you only go into detail about one, make sure you atleast mention both if they're present in the text ;)
I personally wouldn't study just for one of the questions as if you only study for one and the question is really difficult you're stuck with it and you have no other options. Therefore I think it's better to revise both and in the exam decide which question you prefer.
If you have any other questions feel free to inbox me, I'm also studying english language at as level :)