PPE has a longer history, is marginally more work and fewer applicants per place. For employability there's little difference, however the maths and management content of E&M possibly makes it better for finance and consultancy careers, whereas PPE would have the edge for government and civil service ones. However the prevelance of each degree in those jobs may be more due to the type of people who do the degree, rather than the employability.
In short, both are prestigious and very employable, with possibly slight leanings due to the nature of the course.
However no, they're not completely different courses. Many people take them wanting to do economics primarily, and you can do 3/4 of your degree in your chosen subject for each of them. So a PPEist and an E&Mist could have 3/4 the same degree.
As a simple guide to choosing between the two, if you are willing/able to do maths, then it's simply whether you prefer pol/phil or a combination of the two to management. If you don't want to do maths, then do PPE. The economics is identical in both, so the only difference is whether you'd rather do philosophy, politics or management, or skip economics altogether.