@Bowen:<br/><br/>Dr. Doom: Feel's more like a good story line for later. But then again he could be a good start it just depends. He is literally the most threatening villian that lives in Marvel Earth. He is a great mastermind that we can not use lightly! Though there is more to it then his Doombots. He could use an assortment of smaller villains under his thumb. Such as Eddie Brock as Venom, Crossbones, Taskmaster, Radioactive Man, Crimson Dynamo etc.<br/><br/>Loki: Loki was used in the movies as the stepping off point for the Avengers. I wouldnt want to tread there unless we have no better option.<br/><br/>Ultron and Thanos: Are big Avengers story lines, one could be used to start but preferably not Infinity Gauntlet weilding Thanos. (That would be like using Doomsday in a Batman V Superman movie. Oh wait they did that; And ruined the gravity of threats in future movies. :P )<br/><br/>The Kree/Skrulls is probably a good choice from your suggestions in my opinion. It hits a big event without touching to much into some really cool villains that would be better used when we have established the world and our characters more.<br/><br/>So my vote is for : Either Doom or Kre/Skrulls kind of event.