EQ's??

I hear lots of people talk about using certain EQ's for different things but why are they different and what makes them different. I did experiment last night. My go to EQ is normally waves Ren EQ so I took a vocal track and EQ'd it to sound good with the Ren EQ and then placed those EQ settings into Sonnox EQ to hear if they sounded different. They did, the Sonnox sounded cleaner of that makes sense. So my question is when would you use a certain EQ, wouldn't you alway want to use the Sonnox as that's cleaner??

EQ's??