In the Krita, Penance is the foremost. In the Treta, Knowledge is foremost. In Dvapara, Sacrifice has been said to be the foremost. In the Kali Yuga, only gift is sanctioned.
तपः परं कृतयुगे त्रेतायां ज्ञानमुत्तमम्। द्वापरे यज्ञमेवाहुर्दानमेकं कलौ युगे।॥