How to enhance the standard search with custom field?

Hi all,

I would like to know the general optimal procedure to enhance the standard searches like Opportunity search or Lead search.

I've gone through some of the threads here. Some suggest, to add the new field using AET and copy the IMPL class of the search and then code the custom logic. Some say, append the new field to the structure of the search object and then implement the BADI.

I'm actually a bit confused to understand the correct procedure.

Can someone please help me with a generic procedure to enhance the standard search with a custom field?

Thanks in advance.