being happy is important..

Yet, I am curious, what is the biggest festival in Kerala??...is it Onam or anything else?

In Mumbai for example Ganesh Chaturthi is celebrated somewhat bigger than Diwali.

In Bihar and parts of UP, a festival called "Chhath Pooja" is more popular and celebrated more than Diwali perhaps.

I am sure regional/linguistical diversity and local custom prevail even in festivals!