Wow. I'm surprised more people didn't pick Arcane Denial.
I mean, in multiplayer, it's the friendly counterspell. And in single player, it nets you cards in additon to countering the spell.
Above all, it's a nice solid 2 mana counterspell. Plus, it embodies the need for the control player to use strategy and to pick the right moment to counter.
I mean, counterspells add most of the strategy to blue, and all counterspells should be strategy oriented, and not brutally powerful like Absorb and Undermine.
Force of Will ranks 2nd for me followed by Force Spike.