Carstein has it about right here. I do very well with Erebus as a General build... however I either go all general or all Assn with him. You really shouldn't go into a game predetermined on what build you want. This game may have RPG elements but it is not something that should be set in stone before you start. When the game starts you should ask yourself some general questions as well as your teammates.
For me some of these are:
Does the opponent have strong AOE DG's?
What DG's are on their team? On Mine?
Do I need to be an effective pusher? Or Smiter?
Besides enemy AOE, specifically is their Reg a good Reg? Does he use mines etc etc....
...the list goes on but these are just a few of the questions I ask myself. ^
An assn Erebus is not an effective pusher till late game. My General Erebus is an effective pusher the entire game.
One final note: I often play with some, and they ask me what I spec my minion Erebus with that makes him so effective? It's simple for me really; I don't grab all the Erebus skills that people think are needed. My minion build has Mist, Coven, ICA, Morale and lvl 2 bite.. thats it. Swarm and stun are not needed and must be sacrificed to effectively make your minions competetive. This is only my opinion of course... and things do change game to game.
Just try not to follow a specific build from lvl 1 - 20... because depending on your opponent you might want a stronger bite this lvl vice a stronger minion count, or vice versa. Sorry for the winded post but I'm on break @ work and just pretty much jotted this down as I thought it.