The legislative branch is the strongest branch in the Government. This is because this is the branch that determines what becomes the law to govern the whole nation. This is also the branch that consists of large number of government representatives in different fields. Read more on http://www.factmonster.com/ipka/A0774837.html.
The executive branch was designed by the founders to be the weakest branch to prevent the POTUS from becoming a king/dictator. The legislative branch has, by far, the most checks and balances levied against it because it controls the purse strings. The judicial branch is the only one whose decisions cannot be reviewed or vetoed. On its face, it seems the Judicial branch is the strongest.
It's hard to simplify one as "strongest". In theory they counterbalance each other but they also have very different purposes. You can't really say legislation is "stronger" then "court rulings" which are "stronger" than the executive. Each branch can undo the goals and decisions of another if they approach it the right way strategically.
I can tell you that the executive has power now to start wars that it was never designed to have originally and that the last 2 presidents have greatly abused their powers in new ways. Not that they're the only two. Even good presidents like FDR and Lincoln went outside their scope.