I remember someone asked this question about a year ago and there was a very good answer too.
Eldar - Slaanesh
Without a doubt. They created the Lord of Pleasure. Eldar only feel any sensation or emotion in the extremes, and Slaanesh too is about everything in excess.
Orks - Khorne
Again, pretty simple. Both are about rage, anger, slaughter on a galactic scale and wanton destruction.
But which Xenos factions display the attributes of Tzeentch and Nurgle best?
There was an answer but I just can't remember it. Please tell me friends.