One way to compare results is to simply open each site in a separate browser window and manually scan for differences.
But the second way is made by Norwegian developer named Asgeir S. Nilsen has made the task easier at a site called Twingine.
TwinGin
Twingine site contains a blank search form where you can type any search query. When you click Search, the site brings up the results pages for that query from both Yahoo and Google, side by side.It divide the page into 2 column,one side to show yahoo search and another too show google search.
For example ,write
bigblueball in search engine,this will show the result of both google and yahoo search engine.
Result of both search engine for text bigblueball is:-
yahoo:-
pagefound-380,000 within 0.13 sec.
Google:-
pagefound:-135,000 within 0.15 sec.
Check yourself which search engine result is relevent for you.