According to Mahabharata an Itihāsa.:
All the 18 Puranas gives equal benifits after reading them which is same as the benifits of the devotion towards Lord Vishnu.
“aṣṭādaśapurāṇānāṃ śravaṇād yat phalaṃ bhavet | tat phalaṃ samavāpnoti viṣṇoḥ nātra saṃśayaḥ ||” (MBH 18:06:97).
“One devoted to Vishnu acquires (through reading this Mahabharata) that merit which is acquired by listening to the eighteen Puranas There is no doubt in this”.
Mahabharata itself is the Summary of all the 18 Purānas. After completing all the 18 Purānas Vyasa composed Mahabharata which contains the summary of 18 Puranas, 4 Vedas, Upanishad, Itihāsas, etc etc.:
“uvāca sa mahātejā brahmāṇaṃ parameṣṭhinam॥ 67 kṛtaṃ mayedaṃ bhagavankāvyaṃ paramapūjitam। brahmanvedarahasyaṃ ca yaccāpyabhihitaṃ mayā॥ 68 kṛtaṃ mayedaṃ bhagavankāvyaṃ paramapūjitam। brahmanvedarahasyaṃ ca yaccāpyabhihitaṃ mayā॥ 68sāṅgopaniṣadāṃ caiva vedānāṃ vistarakriyā। itihāsapurāṇānāmunmeṣaṃ nirmitaṃ ca yat॥ 69 bh bhūtaṃ bhavyaṃ bhaviṣyaṃ ca trividhaṃ kālasaṃjñitam। jarāmṛtyubhayavyādhibhāvābhāvaviniścayaḥ॥ 70 vividhasya ca dharmasya hy vividhasya ca dharmasya hyāśramāṇāṃ ca lakṣaṇam। cāturvarṇyavidhānaṃ ca purāṇānāṃ ca kṛtsnaśaḥ॥ 71″ (MBH 1:01:67-71).
“Then the greatly glorious Vyasa, addressing Brahma Parameshthi, said, “O divine Brahma, by me a poem hath been composed which is greatly respected. The mystery of the Veda, and what other subjects have been explained by me; the various rituals of the Upanishads with the Angas; the compilation of the Puranas and history formed by me and named after the three divisions of time, past, present, and future; the determination of the nature of decay, fear, disease, existence, and non-existence, a description of creeds and of the various modes of life; rule for the four castes, and the import of all the Puranas”.
All the 18 Purānas are dependent on Mahabharata as said by the sage Veda-Vyasa.
“asyākhyānasya viṣaye purāṇaṃ vartate dvijāḥ | antarikṣasya viṣaye prajā iva caturvidhāḥ ||” (MBH 1:02:380).
“O ye Brahmana, as the four kinds of creatures (viviparous, oviparous, born of hot moisture and vegetables) are dependent on space for their existence, so the Puranas depend upon this history (Mahabharata)”.
Conclusion.: All the Purānas are equal and gives same benifits.
I hope this clarifies all your queries about my comment. Prd..