I think it depends on your facial characteristics. For example, if you've got full lips or an exceptionally strong jawline, you can get by with less facial hair b/c your lips and/or jawline will draw attention to the lower third of your face, balancing the power of a bald/shaved head. If your lips are not so full or jawline not so square, then more hair (full goatee) will add weight to the lower third of your face.
The goal is to provide balance. Bald/shaved heads and above average sized foreheads benefit from a counter balance in your lower third. Once you've achieved that balance, people's attention will be unconsciously drawn to your most important feature... your eyes!
Try looking at other people. When the face is out of balance, your eyes are drawn to the weakest part. When the face looks balanced to you, you're drawn right into their eyes and that's where you wanna be looking.
Also, as said ^, keep all facial hair trimmed short - military short. It looks more youthful and kept. Stay on it about every 2-3 days depending on how fast your hair grows.
I keep my hair (on top of my head) cropped very short. When I grew my goatee about a year ago, I did it just for a change. I got some good advice for how to trim and care for it and I couldn't believe how many compliments it got - from all types of people. Even little old ladies (notorious for hating facial hair) remarked how much they liked it.
IMO, definitely don't go entirely clean shaven. Bald heads with nicely groomed goatees are very sexy, very masculine.