I've been using 0.7 point Pentel Supremes since I began high school

Back when I constantly needed a pen I used to use a Parker espirit telescopic fountain pen, since it was the best small fountain pen that cost little enough that I wouldn't mind loosing, but it was still small enough and good enough for my tastes. More recently since I stopped needing an actual pen with any sort of frequency it just kept getting dry and I just decided to stop carrying one.

This days the only thing that I physically write with any sort of frequency are ttrpg character sheets and for those I just need a good pencil, so I moved to the wsd magnetic 2.0 mm lead holder. I just love it both as a great mechanical pencil and a fidget toy

Not the pen I was thinking of

TUL pens. Super durable as I click my pens from anxiety and I havent had one break on me. Write very smoothly too

I like the Muji aluminum fountain pen.

https://unsharpen.com/pen/muji-aluminum-body-fountain-pen/

Cheap enough that if it breaks or you lose it or some such, you won't be that upset, but writes wonderfully. It is nice to have a pen where you can choose your own ink, and it will accept either refillable cartridges or pre-filled cartridges.

The way the cap posts on the back of the pen is pretty unique as well.

i use Mitsubishi roller balls, real nice and inky, great colours. I'm a lefty so can't really use fountain types.