Stiffness: The most important property. Higher numbers are stiffer. Stiffer strings reduce the trampoline effect, crush the energy out of the ball, and hit a slower shot. However, because the rebound from the racquet is slower, you can swing faster and the net result might be a faster shot.
Tension Loss: All strings lose tension. Most is lost during and immediately after stringing and with your first couple of dozen hits. After that relative stability occurs, but each impact loses a fraction of a pound more tension. Higher tension loss tends to indicate faster loss also. But that is not really important. It is the stiffness of the string as a result of the tension loss that is the key. However, the tension loss number may indicate the comparative duration that the strings may stay at the stiffness value you like.
Energy Return: This is a measure of the amount of energy returned from the total energy that went into the string. Higher return indicates higher efficiency. It does not mean a faster shot. The string may be efficient, but if it is stiff, the energy of impact goes into crushing the ball and not into deflecting the string. Thus there would be less energy to give back to the ball. However, high efficiency may be important to spinning the ball.
Spin Potential, ball COF, string COF: Spin potential is a measure of the sideways “snap-back” of the main strings and the grabbiness of the strings to the ball, both of which, under the proper circumstances, add to spin. The number reported here is the ratio of the string-to-ball grabbiness divided by the string-to-string slipperiness (string-to-ball coefficient of friction divided by string-to-string coefficient of friction). The greatest spin potential occurs with a high string-to-ball COF and a low string-to-string COF. That means the strings will slide and snap-back while grabbing and spinning the ball.