hello, what the most important spec for a IC like amplifier IC
I’m not sure there is a clear answer since the importance of any IC spec is based on the needs of any particular application. Take a resistor, for example. Resistance seems to be the only important spec, but that doesn’t do any good if it burns up in the process of resisting (dissipation rating).
Here is an article written by one of our engineers that can help you get started: [ Op Amp Basics ]. It’s for Op Amps, but it has points you can consider for other types, too.