I have a bunch that I use (no you can't have 'em). Surprisingly (?), it's the cheapest one that I like best: the steel-nib Parker Frontier Flighter bought when I started my PhD, though loading it with Aurora makes all the difference. Got a 14k M400 and a couple other "better" pens, but I still prefer the cheap Parker and have put about half a litre of ink through it so far.
Rapidograph and india ink is where it's at for permanently marking negs and prints though. Nothing else has the permanence to match silver.
Intrigued that you intend to "reimagine" the fountain pen since it's a design that has been hammered on pretty hard by a lot of smart people for over a century... Do you have a specific idea and are looking for parts to execute it?