They should do whatever makes them both most comfortable. It makes no physical difference whatsoever, therefore all that matters is both people's comfort levels.
However, I strongly recommend for people to be more open to the idea of a woman taking the lead, for one reason and one reason alone: When a heterosexual man is not particularly experienced, it is very common for him to accidentally hurt his partner. Then, because we live in a rampantly misogynistic society, we just assume sex is supposed to be painful for women when this is simply not the case.
Taking a submissive position during sex does not make one "less of a man". It does not make one weak. Sex should not be considered to be about power in the first place — it's not a competition! You're supposed to both be having fun! That's all that truly matters.
Of course, this is not the only way to ensure you don't accidentally hurt your partner. Don't underestimate the power of just taking your time, keeping lines of communication open, and using a lot of lube no matter what position you choose.
So, do what makes you both most comfortable. Just remember to be careful, be safe, and communicate.
