I've only used the Cobalt Blue F-C ink, but I've used Tsuki-yo, Fuyu-syogun, Tsutsuji, Kon-peki, Ama-iro and Syo-ro on the Iroshizuku side.
The Cobalt Blue from Faber-Castell is meh, it's not very 'cobalt' in color far as the blue I was expecting, kind of dull. Doesn't seem to have a flow problem but neither did any of the Iroshizuku inks I've used (Fuyu-syogun is a little on the wet side as is Ama-iro, but you kind of need wetness for fuyu-syogun to shade effectively).
Thus far the two Iroshizuku inks I prefer to use is Tsuki-yo and Syo-ro, otherwise the primary brand of inks I like to use is Noodler's (Black Eel, Liberty's Elysium, Blue Steel and Apache Sunset) as most of the ones I use are waterproof. Tsuki-yo and Syo-ro have some resistance.
Far as what's better, where does your priorities sit? What do you want exactly from an ink? What pens/nib combination are you using?
Edited by KBeezie, 06 November 2014 - 23:50.