In terms of career prospects they're basically the same, however, with the Undergrad route you will spend three years learning how to teach, so you'll have more knowledge in my opinion. Also, undergrad is preferred by schools because you've chosen that and are dedicated to teaching, not simply entering the profession because there are no jobs.
PGCE's are great to have after an undergrad degree as it's flexible, but so, so much harder. My friend is doing 70 hours work in 6 days and then sleeps all of sunday to recover. I however do ITT as an Undergrad and I do half of what he does. And the same amount of time in schools.