Rookie Counterbalance question

[superfunk]

Please forgive this rookie question, but I am relatively new to Magic and have a shaky understanding of the rules.

Consider the following scenario:
You have the following cards in play:
Counterbalance (http://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=121159)
Sensei's Divining Top (http://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=194972)
Crystal Ball (http://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=205049)
Voltaic Key (http://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=206332)
Fetchland (http://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=190393)
Lots of other untapped lands (http://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=213618)

You have only a Brainstorm (http://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=184606) in hand.
You have no knowledge of what is on top of your library.
Your opponent casts a 3cmc spell you would like to counter with the Counterbalance.

My question is what is the best play here? Do you have to choose just one of the ways you can manipulate your library and hope the it works to find a 3cmc card that you can put on top, or can you try one method and if it doesn't work then decide to try another before the opponent's spell resolves?

Again, sorry for the rookie question, and thanks in advance for helping me learn this amazing game.

Cheers.

[Valtrix]

Counterbalance is a triggered ability. As such, when your opponent plays their 3cmc spell, and balance trigger goes on the stack. Now, it's just like any other triggered ability. You can respond to it with as many things as you want. It's no different than any chain of spells or abilities that may come up--As long as something is on the stack you always have the chance to respond (unless it has split second!). So, You could top, activate the fetch, then top again, then activate your crystal ball, then voltaic key your ball, use it again, then brainstorm, then top. In particular, fetchland + top is one interaction that makes the counterbalance + top combination so potent, since you get to look at 6 cards to find the correct cmc for the spell.

[superfunk]

Awesome. Thanks for the explanation.