Diamine Registrar's is my go-to ink for work, because it doesn't feather/bleeds through even the cheapest papier.
It's quite expensive though, and I've bought some Ecclesiastical Stationery Supplies Registrars, which is three times less expensive (factoring in shipping costs).
After a workday of using both inks, the differences I've noticed :
1. The colour is virtually undistinguishable.
2. ESSRI is less dry than Diamine, so it's the ink of choice for drier pens.
3. ESSRI does feather slightly and does bleed through slightly, whereas Diamine almost never does.
See the comparison here :
Recto : http://i.imgur.com/gZ5LGby.jpg,
Verso : http://i.imgur.com/3PWCJwE.jpg
The first two lines are written with ESSRI, and the rest with Diamine.
Edited by paviva, 29 November 2015 - 21:20.