This may be the easiest, best, Rider Formation in the game at present.
Fox, Obsidian, Reyn, Dom, and Doc Gray
These Heroes are fairly easy to get—with the exception of Obsidian—and do not require to place high in events, or win one of the lottery type games.
Some might make an argument that both Mars and Marlowe are easier to get than Obsidian, however both of those Heroes provide Troop bonuses, not Rider bonuses, and do better in defending your wall and sanctuary.
Angelo is actually better than Obsidian in terms of bonuses at +5 however, Angelo is very difficult to get, and can really only be won in one of the lottery games.
Importance of Hunt Formation
When you take your troops out hunting either Zombies or Zombie lairs having a good formation with Heroes that match your strongest troops, and the troops that you are dedicating your gear bonuses to, is an important step in maximizing your damage overall.
It is also effective in the Pit, and raids on player sanctuaries. You should always upgrade your troops to the maximum tier that is available based on your HQ level. This will allow you to use your might to its maximum potential.