I think the key is not looking dirty and smelling good. After that, you're going to get some positive and some negative reactions all because of how the girl is.
It's gonna be a personal preference thing for the girl on if she likes a clean shaved face or not. I was clean shaven for 29 years except for a time I had a goatee. Then I grew a beard for No Shave November (prostate cancer awareness activity) and I've kept the beard since then, so I've had one for almost a year now. I've noticed an actual increase in attention after growing the beard. It might be because I'm somewhat baby faced and the beard makes me look closer to my age. I'm 30, and I still get people who think I'm about 25 even with the beard. I keep the beard trimmed down shorter - not 5 o'clock shadow length, but not bushy, either. I suppose in my particular case, it makes me look more mature, and the girls giving attention like mature men.
As for my hair...well, when it was shorter nobody really paid much attention to it because a lot of guys have short hair. When I started to grow my beard, I let my hair grow as well. I trimmed it once for my pharmacy school rotation so I'd look more professional, but it's growing out again. The longer it gets, the more girls go for it. I brush it in the morning so as to not have bedhead or so it doesn't dry in every direction after a shower, but nothing more than a quick brushing. For some reason the longer it gets, the more it changes from straight to wavy so now it's in a weird somewhat wavy stage. No matter how neat my hair may be, someone will always come by and play with it and mess it up. They talk about how soft it is and just play with it, so it doesn't stay neat for long. The girl I'm dating some LOVES to play with my hair, and loves to pull it. When I trimmed my hair she told me I she liked it better when it was longer.