I was checking out my War Games stats on Halowaypoint and I noticed this section under War Games - Game Variants - Slayer:
It shows the two top weapons I have used in Slayer for getting kills. I've had more kills with the DMR than BR, however far less deaths while using the BR so much so my KD spread is superior using the BR than DMR.
While this is a simple stat and there's plenty of variables that could account for the numbers (such as time spent with each weapon, quality and weapon choice of my opponents), it does suggest to me that I might be a better user of the BR than DMR.
I could also infer that I die less in Slayer games when using the BR and accordingly my team will do better as I'll die less - which affords us a greater chance of winning!
TBH, it's a pretty loose extrapolation of the data but you should get my point - your data will tell you about the way you play. If you've got the time, check out your own Halo 4 statistics on Halo Waypoint - you might learn something new about your playing style and be able to capitalise on it!