An ASO (Assistant Section Officer) is a desk-based Group B post in ministries like MEA, CSS or Railways, involving file work and noting/drafting.
An Inspector post (CBI, Income Tax, Excise, Preventive Officer) is field-oriented with enforcement duties like investigations and inspections.
Both are Group B gazetted-level posts through SSC CGL, but inspectors usually get faster promotions and higher-grade pay.
Your preference order in the application decides which post you are considered for.