I think it is very hard to say which card is the most valuable, because there are lots and lots of cards that cannot be priced since they are hardly being sold and are simply off the radar of most people.
I am collecting foil sets 1-10 and many cards I am looking for simply do not show up or are buried in bulk deals when people sell off their collections. Those that still take an interest in the game are after the later sets and promos whereas the cards from the movie block are by and large impossible to price. Once in a blue moon someone like me comes along who is looking for a particular card from those sets apart from the very few prestigious chase rares.
The same is probably true for the price of complete foil sets. They are being sold not very often so prices for those are all over the place as well, since so few people are actually aware of them. It is just too bad that the foils are so scattered and pretty hard to compile

I don't know where that leaves us. We'll probably know more if decipher relaunches the game when The Hobbit opens in theaters...