In my opinion, they are not really competitors. Paredes de Coura has its own vibe, while NOS Alive prefers bigger names mixed with what is around, with no fixed criteria.
This has reminded me of when I was walking to Woodsies last year, ahead of Kasabian. There must have been some daft Eminem rumour because I overheard:
'f**k me, going from Eminem to Kasabian is like going from Beyonce to Emma Bunton'