I wonder if you have changed over time as pens have changed? I like to write with a fountain pen more than I like writing with a ball point pen. I find ball points frustrating when they don't write straight away, especially when you are signing something.
In my organiser I tend to use a mechanical pencil with a 0.5 mm lead which means I can enter my appointments in pencil and rub them our if an appointment is changed or moved.
I have a few different fountain pens some more expensive than others, I've even used some disposable ones!
Filofax themselves sell some very nice fountain pens, but I thought they were a little pricey. Although they do have a good offer on at the moment. (See below)