When in 5th class I got my first pen to write, I was quite excited.
Looking at elders writing with pen made me wonder as to why kids have to write with pencil. A pencil felt kind of inferior in front of and in comparison to a pen. When asked, my mother replied as if she had an answer already prepared, "Anything written with a pencil can be rubbed off with an eraser", and she wrote something, then rubbed it with an eraser, "but something written with a pen can't be. You're learning to write and your handwriting is neither neat, nor stable.
My first pen was a fountain pen. Filling ink in a fountain ink pen was fun, I like(d) Chinese fountain pens. The older I grew, the less I felt the need to write with a pencil, as it had been replaced with a pen. All my daily writing work was now done in pen.
I wondered why did I had to write with a fountain ink pen and not ball-point pen, to which my mother replied, "to get a better grip on your handwriting." Later I tested ball point pen and realized that she was telling the truth. I felt like I could write faster with it but couldn't get a good grip.
At present I use Cello Technotip and it works best for me. I also tried Parker ballpoint and ink pens but didn't really like them much.
After writing for ballpoint pens for some years, writing once in a while with a fountain ink pen feels good, takes me back to those days in 5th class.
Pencil didn't leave my life completely. I used it to make drawings in subjects like biology, and underline in textbooks. I started appreciating pencil since my 9th class because I had lost the luxury of erasing the contents of my writing. Ink erasers are available, yes, and I have used the 'nondust' one, but they work best on ink pen writing and I use ballpoint pens. Besides they don't erase as neatly as a pencil mark can be erased.
Now you may argue in defense of pen that it can write on skin and pencil can't, and I might argue in defense of pencil that one can write keeping pencil upside down, but that can't happen while using a pen!
Well, in conclusion, I use both the pen and the pencil and their combination provides me with a fine range of services.