Both of them are Ascociated with sexuality. Do they involve different aspects of it?
My uneducated opinion:
Mars = masculine, lustful
Venus = feminine, loving
In my opinion, the planets of Venus and Mars are more about masculine and feminine energies than specifically about sexuality.
In astrological charts Mars represents the type of men you’re sexually attracted to as well as your sexual style (and how you take action in life) while Venus represents the type of women you’re sexually attracted to as well as your love and relationship style.
I believe it depends. If you want to attrack a specific woman you can always use the pentegram of venus, and you can always use the pentegram of mars to attrack man. But you should be careful when you decide to using the pentegram of mars because it also means war, anger, lust and passion. Mars is associated with fire so I choose to use both pentegrams when I try to get someone close to me. Another way is that you can try putting a specific demon among those pentegrams/sigils for better results.
It ties closely to Ares and Aphrodite imo. Love and war (and in turn sex) will always be tied.