Airbus clearly prescribes the priorities as ECAM, QRH and if time permits FCOM. Also bear in mind that OEBs when affected by ECAM refer to QRH and as airbus defines the roles to alter as PF/PNF each crew member must have a access to it instantly.
Each airline has a doccument list, at mine the QRH (even on Airbus) is not required, but listed. FCOM allways is.