Frontlines are faster and better than the rest IMO:

- It takes around 10 mins to complete depending on how the battle goes, and you get 5 tomes.
- You can queue as the job that you want to level, then switch inside to the job you like for pvp and you will get EXP on the job you originally queued, so free level ups for you (1,6M exp at lv70 if you win)
- You get PVP points to spend on gear/furnishing/minions, or just sell gear to Grand Company to get GC seals.