what is more important a persons venus or sun sign when it comes to matters...

Venus is definitely more important for initial attraction. Mars identifies the sexual drive and how you act when you're in love. The Sun and Moon are more important for long term relationships.

If you're a female, when you are in love you are acting mostly under your Venus influence. The Sun Sign still matters, but not as deeply as Venus. It's good that you have your Sun and Venus in the same Sign because at least people know what to expect out of a relationship with you. At the same time I know how you feel about not being able to judge personally which effect you're feeling more strongly.

Edit: I agree with Irish about the Sun & Moon being important for long-term compatibility. But I think for a girl, Mars isn't how you act in love, it's more how you act in bed. How you expect or desire to be treated sexually. Venus is how you act in love, how you flirt, etc. For men, Venus is important for initial attraction. Venus is more like what he wants YOU to be, not how he acts in love. For example, if a man's Venus is in Aries he'd be attracted to a woman with her Venus in Aries, because in love, she would become what he is attracted to.

Men identify much more with their Sun and Mars Sign in relationships. If I were you, I'd look at both as an indication of his sexual expectations and preferences.

Actually, I think it's more of the Moon influence rather than Sun when it comes to intimacy issues. The Moon sign/House reveals our capacity for receiving and giving love and affection, pretty much like the Venus sign but more at a subconscious, deeper level. How closed off or open we are to emotional connections with others depends on how well our Moon energies (the heart) can express themselves.

This should preferably be in harmonious aspects with the Venus Sign and/or Sun sign. Venus shows how we attract and receive love and one's flirting style in general. It is more superficial compared to the Moon needs. So when it comes to sexual matters without too much emotion involved, we would be looking more at the Mars and Venus placements.