Is the executive branch the most powerful branch of our government? If so, say why. If not, say the most powerful branch and why. Thanks.

It really depends on who you ask, and in many ways the
time period in which you choose to examine the three branches.  Many people argue that
during George W. Bush's presidency and Clinton's that people worked really hard to
expand the powers of the executive branch.  The checks on executive power are supposed
to be in Congress as they can even seek impeachment if they feel that the president has
really gone over the edge and is doing things that are illegal,
etc.

You can also look at the attempt of FDR to change the
Supreme Court and expand it and add liberal judges and his failure to make that happen. 
The balance of power shifts in different time periods,
etc.

The argument extends to cover the other branches as
well.  Is the Supreme Court "legislating from the bench?" Is Congress overstepping their
bounds when they make certain legislation for the
states?

It will really depend on the perspective and you
could back up either answer yes or no.