Marvel War of Heroes The Master Dr. Doom:
Dr. Doom is the top reward and currently I would estimate that he will be going for close to 400PP each based on what I've seen people offer thus far. At those prices...sell him. He is a great card no doubt, the best for some time probably, but the deck price to make him effective is too high.
To put it into perspective. You will need five Tactic Villains cards to get the most out of him (Tactics boosts + Wild Villains skill), which means you will wither need five of him, or three Dr. Doom and two Magneto wings. Doom and Magneto are the two most expensive cards in the game making the deck cost about 2800ish PP.
For that amount of PP, you could have Five Legend Spideys with close to 1500PP to spare and there is NO defense deck that can beat Five Legend Spideys. This makes it absolutely pointless to pick up a Doom deck over Spidey.
Marvel War of Heroes Oathbound Silver Surfer:
Silver Surfer is the 'runner up' of rewards. Of course the amount of them will be abundant since 3400 will be given out for 301-2000, and another 3000 will be given out for 2000-5000. On top of this, another 100 will be given out to all members of each top 100 orders, so about another 3000-3500. This makes for close to 10,000 Surfers being on the market, or 5,000 UR+ Oathbounds once they are all combined.
Now, the cards skill is awesome and it fits nicely in bruiser decks which have recently become popular as a result of the inexpensive cards. Because of this I would estimate that it sells for 20-25 just because of the sheer number of them. Anybody paying over 30 for them should just wait a week or two, because high level players will be looking to sell and there are close to 10,000 of them.
Marvel War of Heroes Black Leopard Black Panther:
So, Black Panther will be the interesting card. I recommend that players max him and combine him to his final form if they can in preparation of the next event. Black Panther's value will be completely determined by what the upcoming event is. If the next event is a raider event again, you can expect Black Panther's to sell for 10-15PP each. If it's a SHIELD training siege card, don't expect to get much more than 5-6PP out of it.
Marvel War of Heroes Red in the Ledger Black Widow:
Red in the Ledger Black Widow won't be worth much at all. She will be so common that the idea of getting much more than 1-2PP each out of her would surprise me. Even as an event card most players will be pushing to acquire Panthers leaving Widow in the dust.