From the decline of Guptas until the rise of Harshavardhana in the early seventh century, which of the following kingdoms were holding power in Northern India?

1. Guptas of Magadha — Correct. After the imperial Guptas declined, the Later Guptas of Magadha remained a power in northern India in the 6th century.

2. Paramaras of Malwa — Incorrect. The Paramaras rose much later, mainly from the 9th–10th centuries CE, not in the post-Gupta to early 7th century phase.

3. Pushyabhutis of Thanesar — Correct. This dynasty, to which Harshavardhana belonged, was already an important power in northern India before Harsha's accession.

4. Maukharis of Kanauj — Correct. The Maukharis were a major north Indian power in the 6th century and were closely linked to the politics preceding Harsha.

5. Yadavas of Devagiri — Incorrect. The Yadavas of Devagiri belonged to the much later medieval period, especially the 12th–14th centuries.

6. Maitrakas of Valabhi — Correct. The Maitrakas ruled Valabhi in western India from the 6th century and were among the important contemporary powers.

Thus, the correct set is 1, 3, 4 and 6.