About "sepas gozaram "Ive just heard my literature professor say that I never use it I dont know about others :D It sounds alittle bit bookish ( formal) But mamnon is a commonn one And merci too ( although it's french :| )

"Sepasgozaram" is too formal., but in spoken language we usually use "merci" and "mamnoon"

Mamnoon Sohrab:)

Motshakeram Farid for some more detail.