There is an interesting point here, though. Despite the choice of class, the backstory and artwork make each character feel like he or she should be a specific class. Sure, Tomble could be a wildlander, but he's clearly supposed to be a thief. He's even holding throwing knives! Similarly, I have a hard time imagining Grisban as a knight.
I find that Widow Tarha's abilities seem to be at odds with the necromancer class. As a necromancer, you spend a lot of time summoning the reanimate and moving which doesn't provide much time to use the really awesome re-roll ability. Unless I'm playing this wrong, you can't use the re-roll on your reanimates attacks. Its also a tough choice on the first turn wether to summon the reanimate or use the special two-target heoric feat to blast the opening group.
On the other hand, Leoric of the Book's passive damage reduction ability seem to play well with the necromancer's class. Widow Tarha's re-roll ability also seems to be more suited to the runemaster's ability to blow stuff up with blast.