ER-1 Return, filed under Rule 12(1) of the Central Excise Rules, 2002, will have to be electronically filed irrespective of the duty paid in the preceding financial year.
ER-8 Return, to be filed under the proviso to Rule 12(1) of the Central Excise Rules, 2002, by assessees availing the exemption under Notification No.1/2011-CE dated 01.03.2011 has to be filed electronically.
so as per above difination if you are not getting exemption under Notification No.1/2011-CE dated 01.03.2011 than you required to file return in ER-1. If u get exemption under Notification No.1/2011-CE dated 01.03.2011 than you requried to file return under ER-8.