Kaweco Classic Sport

This is my go-to pocket pen. The Kaweco Sport is a small, sturdy pen. It is all-plastic, but it's a pretty sturdy  plastic. The Sport takes the short international cartridges (available from a bunch of makers) but, if you're like me, it also makes a really good eyedropper pen. I've heard that there are some really small converters that you can use with these, but I've never bothered to try.

The nib is steel, but it is gold plated and the tip is iridium. The combination makes for a stiff, but smooth, writing experience. I bought two nib units for it, and both the Bold and Medium nibs are excellent. The Bold is a little wet with most inks, but if you're writing on good paper then you're going to love the shading that it puts down. The medium puts down a substantially thinner line, and it a fair bit less wet. Even pretty thin inks seem to flow well in it.

The only draw back, and this is due to the eyedropper-setup, is that you will occasionally get a drip from the nib. It seems to happen mostly when the ink is low in the barrel or it gets heated up while pointing down. I keep it in my pocket most of the time, but I take care to keep the nib pointing up, and I haven't had any problems. As you can see in the picture below, when you get a little ink in the cap of the clear model you can really see it. I'm sure I could clean it up, but it doesn't bother me so I don't.

I doubt that you would have that problem with a cartridge, but I can't really speak to that.

Goulet only sells one of these, and it's not the clear one that I have, so here's a link to the Jetpens site with the clear demonstrator version.