I've mostly been doing 2-1 for secret garden, as a result my campaign is only completed up to stage 9. Are there any better places to farm?

The special events also don't seem to be that great, you do get a good amount of golden ones, but at 80 stamina a pop its hard to tell whether its worth. Especially since you get very little XP for it, whereas 2-1 is pretty much in line with all the normal quests (~130 xp for 12 stamina).