I keep a supply of retractable PaperMate Ink Joy Medium Point (0.7mm) around, but I prefer to use a fountain pen for the most part. I'm not a fan of affectation, so it's taken me a while to find pens that write well but aren't ostentatious.

I have several Lamy AlStar and Safari pens and swap them out depending on the ink color or line weight I'm looking for.

I also recently picked up a Kaweco Sport pen and really, really like it. It's really small when it's not posted, so it fits in my pocket and seems to be as bulletproof as the Lamy pens.

Also, make sure you grab converters for the pens so you can have more flexibility with ink. I prefer anything that Noodler makes...Heart of Darkness is my goto.

Noodlers Ink 4.5Oz Heart Of Darkness W/Pen https://www.amazon.com/dp/B0015VB4EE/ref=cm_sw_r_awd_Y-8fwbAKG8VQ1

Given the context, I thought it was fairly self explanatory.