This book isn't free until 12/21 (https://www.amazon.com/dp/B07Q5L1CHT) but the software and spreadsheets are always free (http://dudleybenton.altervista.org/software/FluidProperties.zip) I cover every significant equation of state in this book, including the strengths and weaknesses. Which to use depends on what behavior you're hoping to capture. So to answer your question, we would need more information. I have supplied many equations of state for industry, including the latest formulation for steam. Chapter 6 is liquid metals.