I playing around Halo 4, i am current Level 43. This is topic for any of these player who have limited time play game due to their daily life but want reach 50 level fast, but it is for all of Halo 4 player. : )
here secret... just play Spartan ops very often.
-Warzone awards about 2k-3k exp or 4k-6k exp (2x EXP) in each average of 10-20 min of gameplay
-Spartan OPs via find game. playing heroic with 4 coop player. award about 4k each mission in average of 5 min
so here math
in 2 hours total of game play.
Warzone - 2.5k per 15 min = about 20k worth of experience per 2 hour / 5k per 15 min = 40k of exp per 2 hour (2x exp)
Spartan Ops - 3.5k per 5 min = about 84k worth of experience per 2 hour.
so you earn about 2 or 3 time more experience from playing Spartan ops, compare to just playing a Warzone
Source - my Halo 4 game history
well, i play warzone more than spartan ops because I have tons of free time.