Depends on the rest or the team really.  Fahrakin brings more debuffs whereas Longbeard has more direct damage.  Generally speaking Fahrakin fits in a bit easier.  Also easier to book out being an epic.

Zero question. Fatman. Easier to book, and brings valuable debuffs.

Fahrakin in almost every case. Easier to build and book, brings Dec Def, Poison and HP burn.

The all in one CB champ.

both :)