I don’t usually do this. Most of the time I like WAR.
Yes, there are different methods of calculating it. No, that’s not a weakness. Of course it’s not a perfect measure of a baseball player—no single number is. But it is quite obviously a good idea to take the numbers we have (ERA, FIP, K%, BB%, HR/FB, IP, etc.) and use them together in some intentional formulation, rather than just using them willy nilly to justify whatever we want them to justify. WAR can help us compare apples to apples and on the whole it is a useful and spiffy tool.