The answer is pretty simple: All of them.

Here is the reason why:
Related to Forrest Gump you could say that soccer is like a box of chocolates. You never know what you are going to get.

Some of the most acclaimed teams have performed rather poorly and unexciting so far. Just think of France and Brazil the two finalists 8 years ago.

Other games might not have been looking too promising on paper but then the teams surprised everyone (including myself). Think of Tunisia vs Saudi Arabia or Japan vs Australia. Two exciting games to watch.

So to be on the safe side I keep recommending to watch every single game. There is still enough time around to catch up with work. You just have to be a bit flexible;-)