Cazic Brain is probably BiS, as Flowing Thought I is harder to come by for Knights.
https://wiki.project1999.com/Essence_Lens is also a really good option. +5 All Res is worth losing 25 HP/Mana compared to Brain. You'll be capped on STR/STA, so those stats don't matter too much on Brain. You'll mainly be losing out on the 10 WIS and Flowing Thought I from Brain.
Your four options for Flowing Thought I are:
https://wiki.project1999.com/Brain_of_Cazic_Thule (-25 CHA)
https://wiki.project1999.com/Eye_of_Cazic_Thule (-25 CHA)
https://wiki.project1999.com/Buckler_of_Insight
https://wiki.project1999.com/Runed_Coldain_Prayer_Shawl
Both Cazic pieces have -25 CHA. Coldain Prayer Shawl is weaker stat-wise compared to other raid options. Buckler of insight cannot be equipped while you are using two handed weapons.
This is why Brain generally ends up being the best choice for Flowing Thought I. AC is generally lower for Range Slot items anyway. The -CHA part is annoying for lulls, I do agree.