In general, I use a pen. They have a smoother feel to writing & don't have to go through the trouble of finding a sharpener. So what if pens can't erase? You can use this thing called white out to cover your mistakes. However, if your drawing, which I do a lot, I always stick with mechanical pencils. I only use normal #2 pencil if I absolutely have to, like on SATs.
On a side note, I need to write with ballpoint pens instead of gel pens. If your left handed, like I am, Its hard to use a gel pen. Left handers drag their hand across the fresh ink when writing left to right, so it basically gets more ink on your sleeve & the rest of your paper than its actual purpose. Right-handers may or may not know what I'm talking about until they try it, but in terms of motions, righties pull the pen across the paper, while lefties push it.