If you are going for looks in general, ie, cold approaches. 5 o'clock shadow. Looks manly, looks like you normally look after yourself but are on an off day. I've asked many of the women I have been with what they prefer and they all like 5 o'clock shadow. I used to wear one all the time, I did get some complains about being too picky in bed and causing neck rashes.

But really it's what ever you prefer. Another thing to consider is congruency. What fits your overall style?
Lastly, I am a scruffy guy in general. I'm sure other guys wonder how the hell I get girls with such a bushy beard/long hair. I'm growing dreads at the moment. Women always tell me to shave. It's a perfect opportunity to say "NO!" and show who is boss. lol.
One time I had a long goatee. My gf harassed me daily to shave it. One day I decided to surprise her with a clean shaven face. She took one look at it and said: "I don't like it. It's not you. Grow it back!!"
I agreed and noticed I started losing attraction because I was being so compliant. Mind you I was 18 then and younger women are more.... idk... young.