SL33TBL1ND said:
A couple things. Mana Leak is in no way an efficient counter. An efficient counter would be something like Force of Will, or an actual Counterspell. When you're talking in the realm of counterspells, their CMC is more important than their true cost. So Mana Leak and Counterspell both have a CMC of 2 and Mana Leak provides an escape clause. I'll take the Counterspell any day. Or, if you must have a counter with a cost of 1U, use Arcane Denial, especially if you're playing Combo.
Of course, mana leak is outright dreadful when playing in older formats where the original Counterspell or Force of will are available, but in the current standard, Mana Leak is the only 2-CMC universal counterspell. Other "counterspells" are either 3-CMC (Cancel, or the strictly better Dissipate), or have restrictions (Negate, Psychic barrier, Corrupted Resolve, Flashfreeze; or if you're going to a CMC of 1 but even more restricted, you have Steel Sabotage, Mental Misstep and Turn Aside).
It's run as a 4-of in basically every deck that has access to blue mana.
Besides, 3 mana is often plenty for it to be a hard counter.