For the past 3 years I've been writing pencil-ONLY in College, I couldn't stand using pens because I solve pretty much math and I had to use a correction tape everytime I made a mistake, so I looked for an Alternative.
After testing about 10 different mechanical pencils and different leads, including those Rotring Tikky's and a sh**load of Pilot's. Every single one of them had the same problem, the pencil tended to break the leads in the chuck ring after about 2-3 months of use. The outcome was that every once in a while the pencil would start to vommit ( ) little pieces of leads, and break the lead while writing. Then after a while I met my new math teacher, he had a particular pencil that looked like it was ancient! The letters on the pencil had faded, and both the lead and the pocket clip of the pencil had a rusted feeling. The pencil was really old, 4 years exactly, but It's something different in a math's teacher hands. The surprising fact about it, was that it functioned perfectly compared to those damned tikkys!
You are all wandering what that little Pencil was,huh?
It was a Pentel P207 0.7mm lead pencil. So after all this time of searching, I think that the best combo is the P207, with 2B 0.7 leads and the Pilot Eraser.
Also after reading my post it's pretty weird, maybe I'm a bit of psychotic with pencils