This event has concluded, and the guide here is just for archival purposes.
The current Idol Catfight event is essentially the only thing you should be farming at the moment. Starting at around Level 16, you should be able to start taking on the event. You should be able to do at least the beginning of the Idol Catfight questline, which should unlock the Free Quest F-S1. It’s a good idea to burn a few Energy Potions and Assault Tickets here to get a few levels, then Boost your units to your current level. Then, continue on the Idol Catfight questline until you unlock Free Quest F-D1. You can essentially spend the rest of your Energy here from now on, and even use Demonite to recharge Energy. Higher level quests give the same ratio of Silver Coins/EXP per Energy, so farming this even when you’re way overleveled is still perfectly efficient. Thanks to fish_fucker69 and Ignite, we’ve found that F-D1 is more efficient than F-B1 by about 60%, and more efficient than F-S1 by about 50% in terms of farming event materials for Potential/Evolution. F-D2 seems to have the same rate, so it’s okay to stick to F-D1. Farm here until you have enough Star Charm to get whatever you want from the event (it’s recommended to get at least all the Idol Iblis essences at roughly 90,000 points, the rewards from this event are a lot more worth it than farming outside). In terms of priority, clear the event shop for D1 first, then S1, then B1. If you’re planning to go for 5* evolution and want to spend some cash on the game, it would be optimal to grind out 150,000 points for Flawless Spirits, which are ordinarily very difficult to come by.