The Thousand Sons were the very first tournament-specific army I built, based around the Index Astartes list in White Dwarf. Why did I pick them? 3 reasons – they had two wounds each; their possessed could charge 12"; their dreadnoughts didn't go crazy.
I created the army list based around three units of eight marines plus aspiring (sorceror) champion. This was joined (as far as I can remember) by a unit of 9 possessed, a dreadnought and a land raider – all led by a Sorceror Lord on flying disc. From memory they did ok, but not great (mostly due to my naive tactics). I never got to buy, build or paint the Dred and LR so my Templar rented out theirs for the occasion.
It is my aim one day (once I tweak my Bezerkers and finish my Nurgle) to revisit these Thousand Sons, give them the paint job they deserve and maybe add a few more models.