One should worship Lord Viṣṇu or His devotee for spiritual advancement in knowledge, and for protection of heredity and advancement of a dynasty one should worship the various demigods.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
धर्मार्थ उत्तमश्लोकं तन्तुं तन्वन् पितॄन् यजेत् । रक्षाकामः पुण्यजनानोजस्कामो मरुद्गणान्
dharmārtha uttamaślokaṃ tantuṃ tanvan pitṝn yajet | rakṣākāmaḥ puṇyajanānojaskāmo marudgaṇān
SB 2.3.8