Roulettes..
Frontlines is fast and good exp.
Alliance raid pretty fast queues(sometimes) have ok exp but you can get some materia so the $$ is nice.s
50/60/70/80 Dungeons and Trails can be fast if you have unlocked em all but exp isn't worth it sometimes.

If you want to grind without queues.
PoTD/HoH is decent to 71
Then Bozja to 90

My personal choice...
70->80 Roulettes and do something else youtube or w/e
80->90 When I have rested exp queue the dungeons you have 80+ (not the roulettes) then spam fates while I queue. At like 83 I was getting 5min queue and solid exp.