I noticed my spm hasn't been going up anymore and didn't think to attribute that to playing gun game and stuff recently.... Good to know.
I don't think there is any stat in game that will show you how good a player is.
To many factors to concider.
Diamond camo's (can be a real pain and hurt your gameplay)
Goofing around (trolling)
The stats you can view are completely decieving.
You would have to find someway to evaluate the player's team and enemies to weight their stats. Without a ranked ladder it would take a lotta reviewing of games and spreadsheet work to figure out how good someone is.
Easiest way to gauge how good someone is? Play with them for awhile.
Short answer: SPM.
Longer answer: There is no true reflection (due to party boosting).
The number of bars they have for connection.
How happy they sound when they are playing the game.
Depends on the game mode. I play hckc 99% of the time and find that an even k/d and w/l shows they play the objective as a team player.
My stats, kd-1.4 wl-1.41 spm-314