*Ahem* Okay, what is a "nice" penis, I can address that, I've seen a few.
In my opinion, a nice penis would be one with the following characteristics:
Head larger than the body of the penis, larger enough so one can see a clear profile. This is especially nice (for me anyway) if you can feel the head going in seperately from the rest. I suspect this may have been what your female friends were referring to (?). It just feels good, to me anyway.
Good proportions of length vs. width, well-formed look. Not too skinny or fat, etc. I've seen some that had kind of a "blobby" unformed look, wasn't into that.
Nice sturdy construction, doesn't taper too much towards the head, which always looks kind of odd to me.
It's good to see some veins or other evidence of "strength" and ability to do the job at hand - a smooth, innocuous-looking penis seems like it might peter out or be wimpy somehow. On the other hand a huge bush of hair growing off the thing is a little too "manly" for my personal taste.
Not warty or too wrinkly, not too bent/crooked. A little crooked is fine but a lot looks disturbing. If it bends down dramatically for example, one suspects it might poke in all the wrong places.
Skin tone not too dark in comparison to the rest of the body - some difference is completely normal but sometimes they are so much darker they look like they came off a different person.
Nicely proportioned to the rest of the body - i.e. a short stubby penis looks strange on a tall skinny guy, and vice versa. Nature is generally kind on this regard but there are always those exceptions that make you wonder.
That's it for now I guess...I'll be curious to see if the other women agree with me.
