Brahma is the secondary creator, but Krishna is the prime cause of all causes as Brahma himself states in his treatise called as Brahma Samhita.
Śrī Brahma-saḿhitā 5.1
īśvaraḥ paramaḥ kṛṣṇaḥ
sac-cid-ānanda-vigrahaḥ
anādir ādir govindaḥ
sarva-kāraṇa-kāraṇam
Kṛṣṇa who is known as Govinda is the Supreme Godhead. He has an eternal blissful spiritual body. He is the origin of all. He has no other origin and He is the prime cause of all causes.
vedabase.net/bs/5/1/
One can worship various demigods in order to achieve various purposes, but in order to achieve any or all of these or to be free from all these material desires, ultimately one is asked to worship the Supreme Personality of Godhead, Krishna (purṣam param).
2.2-7: One who desires to be absorbed in the impersonal brahmajyoti effulgence should worship the master of the Vedas [Lord Brahmā or Bṛhaspati, the learned priest], one who desires powerful sex should worship the heavenly King, Indra, and one who desires good progeny should worship the great progenitors called the Prajāpatis. One who desires good fortune should worship Durgādevī, the superintendent of the material world. One desiring to be very powerful should worship fire, and one who aspires only after money should worship the Vasus. One should worship the Rudra incarnations of Lord Śiva if he wants to be a great hero. One who wants a large stock of grains should worship Aditi. One who desires to attain the heavenly planets should worship the sons of Aditi. One who desires a worldly kingdom should worship Viśvadeva, and one who wants to be popular with the general mass of population should worship the Sādhya demigod. One who desires a long span of life should worship the demigods known as the Aśvinī-***āras, and a person desiring a strongly built body should worship the earth. One who desires stability in his post should worship the horizon and the earth combined. One who desires to be beautiful should worship the beautiful residents of the Gandharva planet, and one who desires a good wife should worship the Apsarās and the Urvaśī society girls of the heavenly kingdom. One who desires domination over others should worship Lord Brahmā, the head of the universe. One who desires tangible fame should worship the Personality of Godhead, and one who desires a good bank balance should worship the demigod Varuṇa. If one desires to be a greatly learned man he should worship Lord Śiva, and if one desires a good marital relation he should worship the chaste goddess Umā, the wife of Lord Śiva.
SB 2.3.8: 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.
SB 2.3.9: One who desires domination over a kingdom or an empire should worship the Manus. One who desires victory over an enemy should worship the demons, and one who desires sense gratification should worship the moon. But one who desires nothing of material enjoyment should worship the Supreme Personality of Godhead.
SB 2.3.10: A person who has broader intelligence, whether he be full of all material desire, without any material desire, or desiring liberation, must by all means worship the supreme whole, the Personality of Godhead.
SB 2.3.11: All the different kinds of worshipers of multidemigods can attain the highest perfectional benediction, which is spontaneous attraction unflinchingly fixed upon the Supreme Personality of Godhead, only by the association of the pure devotee of the Lord.
SB 2.3.12: Transcendental knowledge in relation with the Supreme Lord Hari is knowledge resulting in the complete suspension of the waves and whirlpools of the material modes. Such knowledge is self-satisfying due to its being free from material attachment, and being transcendental it is approved by authorities. Who could fail to be attracted?
http://vedabase.net/sb/2/3/10/