Not really good for tournaments because the ELO banned cards are -2 points each, every game. That can cut down your score a lot. If you want to keep GHEIST/Nightmare I suggest replacing Toro and Zero Dead by a 3 star and 4 star, and taking out Kolos and putting in a 4 star like Azgroth maybe. But the best for DTs is Montana and maybe Uppers. I suggest trying those clans.
Well, the only ones that cause the -2 points are the ones that are staff banned. So Kolos would cause it, but not Z3r0, Arkn, or Toro. They're okay. (If you go up top to "The Game" tab in orange up top, and click the rules button for tournies, it'll show a list. That list won't change from week to week, but does change occassionally like this week).
Right now, we're on the verge of playing against a LOT of Pirannahs. I would suggest *against* playing Montana & Uppers just because they lose some punch without their bonuses (especially Montana). Skeelz might be a good choice too...
Nightmare is a fine choice, just because it's a wash. Obviously, you would want to replace Kolos, but other than that, play with what makes you feel comfortable, and as you learn & see more, you'll make your own adjustments.