I prefer Mono-clan because you never have to worry about not getting your main bonus. Also Mono-clan is the only way you can really use a Leader well. You can also add in a powerful ability offclan card like Veenyle, Uranus, Hawkins, Smokey or Andsom without losing bonus. Of coarse you get more variety and combinations with 2 clans and don't have to settle possibly for weak clan cards (Like K Cube).