Chirper Events are the easiest but if you run out, you'll pretty much be forced to use them in battle... a lot of battles...
I have never bothered putting any effort in figuring out what causes a chirper to happen but from what I see, things that 'may' affect it are the shares, how far you are in the story, current lily rankings and the previous chirper you have completed, something like a prerequisite.
All I basically did end game was go to a town, spam click one of the main characters on the chirper til and event popped up. If nothing appeared after a few clicks. Move onto the next character. Rotated around town and back a few times. That's how I did mines. Ended up getting everyone to Rank 5 Lily other than Blanc, Rom (or was it Ram) and Vert.
Since I didn't focus on Lily rankings and chirpers til end game, some of mines were... really weird, like I got a event where Gear, IF and Compa were talking about how they needed to save Neptune. I had already saved her.