What alignment would you associate with each class

[Trask]

Vengeance always had a chaotic neutral flare to me. So, maybe Chaotic Neutral with Good tendencies? (to really call back ideas that are NOT at all present in 5E).

@OP, Monster Slayer feels Neutral as a baseline, and then depending on what they concentrate on, add an ordinal. So, anti-Undead or Fiend is probably NG. Anti-monstrosity is probably TN or LN. Anti-metallic dragon, NE; anti-chromatic dragon, NG; anti-abomination, NG all the way to LG depending.

I still like Chaotic Good for Vengeance because they are still righteous, CN doesn't describe a righteous character IMO. IMO chaotic alignments tend towards "Might Makes Right" on the evil end and "The Ends Justify the Means" on the good end.