For dye-based inks, I have the most bottles of Diamine and their inks have been solid so far. I also enjoy J. Herbin's Shimmer inks (which I only use with my Pilot Prera since it has an italic nib that helps lay down far more ink than my other pens - I generally go for EF (0.2 mm) nibs) and while the ink is interesting, it doesn't give as much shimmer as I would like to see.
My favorite inks are the pigment-based, of which Platinum's Carbon Black is my most used. You do want to make sure that you clean your pen out well after using a pigment ink as they can dry on internally and be quite a hassle to clean afterwards (potentially requiring your to disassemble your pen and gently scrub the feed with a spare toothbrush to unclog the ribbing). However, I personally love that it is basically water proof once it dries, which means that I (being a lefty) don't smudge my handwriting nearly as much with them - even on hot days where my hands are a bit sweaty.