What are the best available metrics for measuring performance/value. What are their individual strengths and weaknesses? Which do you favor and why? Do you use a mix or a composite number between multiple metrics (for WAR, for defense, etc.)? What's missing from the best available metrics and how do we get there from here?
Feel free to break this down into distinct areas of hitting, pitching, baserunning, fielding and, of course, overall - "uber" - metrics. Curious what the consensus is here and, more importantly, by sharing perhaps some people can learn about new metrics they were previously unaware of.