The game is way to Easy until you get to End Game

[Sadana]

Wait, new character or new classes? If the first, at least you have all the quests available besides hunt log and dungeons. If you watch all the CS, maybe you'll catch some lore you didn't the first time. Or you could skip them all and save yourself a LOT of time this go round. If you mean new classes on the SAME character, I suggest leaving side quests for this very purpose. Doing MSQ and dungeons is more than enough to get to 50 in a short time on your main class. Side quests, dungeons, hunt log, FATEs, and leves will help to level other classes. Go with friends too! Makes things way more fun.

Personally, I like leveling... way more gratifying than throwing myself at the same primal or coil turn over and over.