Rival Wings is currently the most efficient way to farm tomes. It's fast and allows you to level your jobs, earn seals, progress through the PvP series, and work toward the mount achievement. However, the tome rewards are primarily items players already have or don’t need, so many may not be inclined to set aside the new games for it.

Fyi: Primal is considered the go-to DC, last I heard for RW, during prime time.