Which faction poses the greatest challenge for the Dwarves?

Luck is certainly a good thing, but is it worth taking up an entire slot for it?? And by the way, is Avenger for the Elves? Haha, one less Elf. Never mind, luck can be increased not only through artifacts but also through various buildings on the map, so why learn it just for rushing? And besides, Necromancer rushers aren't that great (although maybe they are). I used to like Druid, but not so much now.
Naadir is clearly better.