I had 3 months in Ibiza back in 2003 and rented an Apartment in front of Pacha and went to most Subliminal and Pure Pacha nights.
Whilst were both excellent, as Pure Pacha is on a Friday night i found the place was two full and thus not able to have an enjoyable night.
Fridays are always going to be the busiest night as dont forget the locals like to go out two, however comparing it to when Ministry of Sound used to have the Friday nights, Pure Pacha is just rammed full.
Then again, if your just there for the atmosphere and dont need much room to dance then it will be fine.