Most favorite events: Nidhogg event, needless to say it's my most favorite one for extremely challenging and give you rarest rewards, the super ampules.
The close second is Nae-chan feeding. Because Nae-chan is super cute that's why!

Least favorite events: Well... none? I can partially read Japanese so I know who to bet on so swan boat is not a problem, if anything it's a relaxing event I can stay back and enjoy lots of currency while spend stamina on other stages. Maybe treasure rally or card flips due to intense stamina cost if you want to full clear and not because it's boring or tiresome.