A penis can be long and narrow, or short and girthy, or both, or neither, in any combination.  
Not to mention curves and the head.  

One civie lady told me it's all about girth.

Xoxo

If the question is asked. It is both. But girth is the biggest issue and results in the most number of rejections.

....... I have an approximately average length penis. So, the ladies I see can't get away with padding my ego about my length, so they pad my ego about it's girth.  
The only reason I have measured was this.
The night before a blindfolded and bound BDSM session, Mistress called me and told me to measure my cock's length and girth while hard. She talked me into an erection on the phone, and i measured. She then directed me to not jerk off. She wanted me to show up with a case of blue balls. I followed Mistresses orders.

For those of us petite ladies.  The length is not as much an issue (for myself, anyway) as the girth, ouch!  

I love the feeling of being penetrated, and a good girth hits all the right spot for that. Too long lengthwise can hit the cervix and hurt. Woman are more maleable horizontilly vs vertically, just from a physiological perspective.

... I'm not into soda can girth penises but super skinny ones aren't fun either (in the front or the back).  
In any case if I am i'm wanting to know about both ... moreso the thickness.

I had a lady tell me that too long wasn't any fun for her in cowgirl because she had to ride sideways to keep it from hurting. But she told me I had the perfect fat cock for riding as climbed on top and so elegantly demonstrated for a while.

When you feel you need to dislocate your hips to get it in there....Lol