Which is harder to get in to, Mechanical or Electrical Engineering?

You need to check each specific school. It does look like, at colleges where EE does not include computer science and engineering (CS or CSE), EE is likely to be the less popular and less selective one if it matters (but there is no guarantee on that for a specific college without specifically checking that college). If EE does include CS or CSE, its popularity may be increased by those primarily focusing on CS or CSE.

Where students enter undeclared or engineering undeclared, also consider whether there is a secondary admission process to specific majors, and whether ME or EE is more competitive: http://talk.collegeconfidential.com/engineering-majors/2174743-first-year-engineering-programs-secondary-admission-to-major-criteria.html

But really, you should be considering which whether ME or EE is better suited for your academic and career interests.