Maplestory Reboot Ice Lightning Burning Cernium Eastern City Ramparts in Battle 3 - 18330 kills/hr

Arguably the best training spot from 260-265, and Grandis familiar farm (as of the GO WEST update). However, this rotation is a little more involved than a map such as Burnium library 6. I would personally recommend library 6 for its "lazy" factor, but if you want optimal rates then you should be in this map.