I went through a fountain pen "phase" in high school. Used all kinds, from actual "quill" pens that were basically a feather, to the pens you dip in the ink bottle, to the lever pen refills, to the cartridge refills that use the ink well, to disposable cartridges. They were rarely nice to write with because they either smeared ink, or leaked, or just scratched on the paper as I wrote. Still, I stuck with many attempts because it was, well, fun.
I'm more practical now, and use disposable pens. I'm like wodin - I keep a lot and scatter them around. I'm absolutely convinced my wife eats them. Come to think of it, she must eat my umbrellas also!
Anyway, I've tried expensive pens, gel pens, fountain pens, etc. I really like a nice pen. But in the end, my own personal taste seems to fall toward certain mass produced cheap disposable pens. I'm glad because they are cheap, but I'm disappointed that (in my experience) the more expensive pens only seem to look nicer, not function better. And, in fact, seem to be less consistent in the quality of the refills.
Btw, I'm really impressed with those of you that always write with a fountain pen. I couldn't deal with it all the time even if I liked it better. But with all that use, you must certainly have found some nice ones, or you would have given up by now.
As an aside, for some reason I really also like those small metal "half-size" pens that fit easily in your pocket or purse, and have a metal cap that goes halfway down the pen. Hard to describe, but the only place I've found them is from my realtor, who was kind enough to give me several!