I have just received the dagger from Scanthril and am ready to go back to Ishad N'ha and get an assassin. My question is: which character(s) should I have become the assassin? The most logical choice would probably be my Ninja. She's an elf, who started as a rogue, then became a bard, and is now an 11th level Ninja. Problem is, she's my only female character. So would it beehove me to save her for Valkyrie-dom later? I suppose my next-most-logical choice for assassin is my male Gourk barbarian. I also have a human samauri, dwarf paladin, oomphaz warlock and whiskaz monk (all male). Any advice?

Yes..here is my advice: Don´t spend too much time in this "personal" quest. I have finished the game without ANY of this special profs (at the end I got Samurai, Ninja, Barba, Warlock 2x and Pala).

The description of the special profs in the book are cool, but finally they are totally useless !

Taski

So you're saying it doesn't matter what the heck I do? Yeah, I suppose the game's easy enough as it is, eh? Hmmm... Anyone ELSE got any advice?

Some points which may help.
1. You can't go back to a previous role. So save the best ones till last. Don't promote anyone to Assassin unless (a) you are happy to lose this later on, or (b) you don't intend to promote her/him ever again.
2. Improving a high level role is very slow ( 13th level to 14th level takes forever) and gains only one spell and a couple of skill improvements, whereas changing to a new role then promoting up to your best level is very fast, and brings lots of skill and spell improvements.
3. By the time you have the opportunity to get a Zen Master or Valkyrie you are just about ready to face Cet in the final showdown anyway. Be prepared to either forget these roles, or to put the Cet Quest on hold while you sneak back to town.
4. Progress in spell schools is hard if the role doesn't support those schools. So converting from Priest to Monk is fine for Spirit magic, but puts a real brake on your Vine Spells.