Dear Aspirant,

Income certificate is always preferable and also sometimes it is mandatory as a proof for income. No other document is entertained by authorities other than income certificate. Moreover, income certificate is not something you made once and can use it forever. You have to make it annually or depending upon your state's norms. 

It is because of the fact that the income of the person is not the same for his lifetime. You have to produce the latest income certificate during the document verification.

Hope this helps.

Thank You.