The trailer was edited in PAL format, so the PAL version is the better of the two.
They're small and both should download fast.
Both versions feature an extra scene with Tegan and the 6th Doctor from Jim'll Fix It, that didn't make it into this trailer.
The PAL version also has a secret extra audio track of the trailer without music, that's not at all in sync for some reason (running slightly too fast). Hence it being secret.