What to wear?

Well, got a local tournament, coming in 2 weeks, and I'm torn on what to take.  The last game with my Tau was really bad -vs- Dark Eldar...  I'm leaning towards the boyz or Nids.  The last 2 tournies have had IG, DE, Grey Knights, and 3 SM armies.  All are the bane of both lists.  I could do mech-Dar, but, until a new codex comes out and gives us cheaper units... I don't know.  This is the 40k Addict....