There are 3 classes you should really consider doing next
1. Reaver
2. Reaver
3. Reaver
I have indeed done this. Including the latest list of all my promotions here. I think it is curious that I have so many agent challenges completed but most of the remaining agents average around 15 missions completed each.
Silent Sister - 44
Arcane Warrior - 43
Reaver - 38
Archer - 36
Avvar - 32
Keeper - 32
Legionnaire - 25
Elementalist - 22 (Need about fifty more missions to complete the 250 mission challenge)
Hunter - 13 (Only 87 missions completed)
Alchemist - 4
Templar - 4
Saarebas - 3
Assassin - 2
Necromancer - 2
Duelist - 1
Katari - 1
Virtuoso - 1
I played with the Katari a little bit, and I am not really that impressed. I am thinking of just focusing on:
Constitution - Avvar and Reaver, with an occasional templar mixed in
Willpower - Actively finishing Elementalist, but will likely keep playing Elementalist and add in Saarebas. Arcane warrior for when I promote the rest and want to keep running nightmare.
Cunning - Planning on playing the Duelist / Hunter. With the silent sister again as a stand-by for NM when the rest are promoted back to level 1 and I want to keep running NM.