Anomen is effectively pure class, his handful of fighter levels has no impact on his capability as a cleric.
Viconia is completely pure class.
On the mage side, you have Nalia, Edwin, and Imoen. Nalia and Imoen have a smattering of thief abilities, but like Anomen, this doesn't negatively impact their magery (in fact, enhances it, since it lets them use shortbows and gives them better hitpoints).
Edwin is far and away the best mage due to his conjurer spec and his special amulet which gives him bonus spells. Except for his hitpoints (which are terrible), he's a better mage than even your own character could be. Similar situation with Haer'Dalis as a blade...his tiefling resistances and ability to 2-star short and longswords give him a big edge over any character you can create.