I still like the uni-ball power tank. It's a $2 disposable pressurized pen.

It looks to have less metal than a pressurized refill so it seems possibly even more sustainable than a refillable.

It solves the problem of all your pens being dry when you suddenly need one after a few weeks of not using them.

And they have a nice rubber grip, and you can see the remaining ink.

Fountain pens are nice for extended writing, but for a modern 90% paperless lifestyle, it's hard to imagine something better than the power tank.