I've been sampling various combinations of ink and fountain pens. It's a huge surpise how different pens with the same ink give wildly different results. Using my TWSBI 540 pen with Noodler's Black Swan in Australian Roses ink gives a nice even burgundy line. Put the same ink in my Noodler's Ahab pen and you get a gorgeously shaded line from black to burgundy, but it's so wet it takes a while to dry on the paper. I picked up some blotting paper to use with the Ahab, and it helps, though some of that gorgeous shading disappears. The Ahab gets most used in work on a Rhodia pad where the paper is thick enough that the ink doesn't show through.
My ink sampling notebook has a few lines in it from each pen and ink combination. The Noodler's Ahab tends to be dark because it's an ink hog. The Shaeffer Prelude writes light, so it's not the best for colour sampling. The TWSBI 540 would be a good sample pen, but it's a piston-fill and not great for getting into the tiny sample vials. So my sample pen might be the Ohto Dude, a pen that takes only cartridges. I have a blunt syringe that I can use to fill empty cartridges from the sample vials, and a bulb syringe I can use to rinse out the pen afterwards.
Another interesting pen is the J. Herbin Refillable rollerball, which takes cartridges and might be a good sampling tool. I love the idea of a rollerball but with cartridges, and with the syringe, I can put any ink I chose into the cartridge.
Handwriting with an ink pen forces me to slow down and pay more attention to how I'm writing. I've made a few changes in how I write because of these pens: my capital "H" is more stylised, I'm trying to form the lowercase "s" by always coming off the paper before I start it, my lowercase "i" has a little extra line at the top so it doesn't disappear, and the lowercase "b" is formed as a stick and a separately-drawn curve instead of one malformed stroke.