The Thousand Sons Chaos Space Marine are much better! Better psychic power, muuuuch more psyker in the army. Ulthwe only have the seers and some Warlocks. With the Thousand Sons you can have a 9(powerfull) psyker HQ, Each of your Champion are Psyker, and your basics troops have 2 wound. B) C'mon, you know you want them!