Lamy Safari fountain pen, just bought it the other day, only £12 and seems like it'll be cheaper in the long run than constantly buying an entire new ink pen.
After a day or two of getting used to it, it feels amazingly nice to write with and is like constantly having that 'new pen' feeling when writing, you don't get that thing where it just writes like **** when the ink gets close to running out - it just writes fine and then suddenly starts running out and writing badly, then you change the ink and it's fine.
Before that though, Zebra Z grip gel pens (probably keep a few of these as backups in the exam) and before that, Uniball ink pens.