Well, the Wizards were very nice, especially with the specializations (I used to be the Master of the Crypt for a while there).
But for me, Blacksmiths there have to take the cherry, compared to them, Genesis smiths are like crawling babies vs Usain Bolt.
And don't get me started on Khiraa, but that was Genesis stuff first, so it doesn't count

Other guilds were pretty damn cool too, maybe except racial guild for ducks (sorry, ducks were ruining the mood for me there) and this ogre-like tree lovers... Forgot how they were called.
And the domains... Well, I don't really remember their names. France was pretty neat, the area with Darkleaf forest, this place where elven racial guild was (and I think that dwarven guild was there too)...