I'll take whatever I have available, but if I have an option I'll take a (preferably mechanical) pencil over a pen. I make a ton of mistakes when I write. Even without syntax errors, my handwriting is still chicken scratch, so I have to change letters just for legibility sometimes (my lowercase r's sometimes look more like v's, for instance).
This is how I am. My 2's actually like look mirrored 6's. I do take whatever is available, but as you said, I prefer a mechanical pencil. I use them literally all the time. I also have to use pencil grips because I grip my pencils with so much force and also write with force. Without the grips, I would get a wicked cramp in my hand/wrist/fingers. :c The pencil grips somehow take the pressure off and make writing a little less painful for me.
For most things I use a pencil, and it's always the Bic mechanical pencils with the grips. They have great erasers. {XD
Bic is my go-to mechanical pencil. I bought a whole pack of them at Staples, but they don't have grips. So, I found an older one that was broken that had a grip on it and stole it's grip for the pack I got of them. Bic are the best kind for me. I also use 0.9 lead as well because again... I grip hard and write with a lot of force. I can't really help it. It's like some sort of odd impulsive I have or something. For pens though, I'll use basically anything as long as it's not papermate ones. They are far too cheap to me, and maybe I just have bad luck with them but... they always run out on me after writing a few words. ><
Here are some of my favorite pens/pencil:
The first one: Again, as I said above... this is a Bic pencil with a thick, clear, glittery pencil grip (from another Bic one that had a grip, but it was broken). I have others like this as well. It's a 0.9 one, and I adore Bic for their mechanical pencils because I use them constantly!
Second one: This one is neat because it's made from recycled materials like plastic bottles. I have ones in blue, black and red too. I got them years ago at Walgreen's during the back to school sales. I don't use them much, but I just thought it was neat they were made from recycled materials. You don't see that everyday! This one is a Pilot pen, which in my opinion is a pretty good brand.
Third one: I LOVE LOVE LOVE these. I use these more for my VAs when they sign my autograph books. They are so fluid-like and come out extremely smooth and such. They are called Uni-ball. I seriously adore them. They hardly ever run dry halfway through writing things. I like having a bunch of these because of how smooth the ink is when you write!
Again, I'll use anything that's available in most cases. However, there's always the case where the pen I've grabbed has died. So, it's often frustrating to find one that actually works. There are ton of the lying around, and they die because they lose the caps and get really old I think.
Luckily, I take pretty good care of my pens/pencils in a
Death Note pouch. :3 Well, at least I have been recently. XD I figure if I keep them in this pouch that I'll know where exactly they are. So, if I need one of them... I can just access them in my little pencil bag. ^^
To Death Note fans who ask: I got the pouch at Saboten, my anime convention. Unfortunately, it was a long time ago though. I'm not sure it can be found again sorry.