No polish and shorter length is my personal favorite. I don't like longer myself, but just about any color nail polish is fine if you want to wear it. Any shade of red is my least favorite, but I also don't like the color red in general.
When I was younger, with my first girlfriend, I was more adamant about the fact that I didn't like nail polish and it was a real point of contention for us. In my slightly older age I understand that a girl should do whatever makes them feel good. So I hate to sound cheesy or something here but you should do what makes you happy with your nails.
Between the 2 I would like long nails with neutral colors. However, depending on the complexion of your skin, those dark colors like dark purple, dark brown, dark maroon also look good with long nails.