This is probably the one subject in the world in which I could be considered an expert. I'm a professional artist, and I draw/ write pretty much all day, every day- with pens. I have tried and used almost every pen on the market- worldwide. I go through literally thousands of pens and markers a year. I carry my pens around in stuff-sacks, I use so many of them. The best PERFORMING pen, in terms of writing smoothly and evenly- is the Uni-Ball Vision Elite.
They're not the fanciest, the prettiest, or the most expensive pens in the world, but they do write the best. You can find them almost anywhere.
I also really like Sakura's Pigma Micron series.
I go through those things like popcorn. They're not the best for writing, but for drawing, they can't be beat.
I really wish there was such a thing as a fancy, high-quality pen that performed well. I would be all over it if there were. I own several of the Fisher Space pens, not to mention high-quality/ expensive fountain pens etc., and nothing comes close to the humble Uni-Ball Vision Elite in terms of line consistency. I like fountain pens a lot, but they can't use high-quality inks (all fountain ink is dye-based) so they're useless to me. If I want fountain pen-type lines, I have to go really old-school, and use dip pens, which I do a lot.