I use the Pilot Hitech 05 Rollerball pen. Have been using this since my school days so my hand is used to it. There are two drawbacks though:
1. It gets over pretty fast.
2. Grip is a problem during a 3 hour exam but I recently discovered that you can get a pencil grip separately and attach it to any pen while writing. I find that solution better than changing the pen I have been using for years.
