As per my knowledge ISA is for System audit whether system audit in bank or in any firm or at corporate level.. There is nice scope of ISA if you are sure to go ahead in that field then CISA is also nice. ISA is the course by our institute which we can do after passing CA only but CISA is international course of System audit which we can do any time. and value of CISA is more than ISA but at the same time Cost and Effort to pass is much higher in CISA. you can do any course both are for system audit and nice scope is there if you want to practice. i m also planning to do CISA.