White widow has one of the highest THC percentages of all strains, that is one reason why it is so valued, another being its sexy leaves

Northern lights and Ice are great strains too.
You can choose a strain from either the Sativa or Indica group depending on what kind of high you want to get too.
When smoked, sativa gives a clear, up, cerebral high while indica produces a 'stonier' more physical hit.
For what I think you're asking, I would go with a sativa strain or a mix between the two.