"Is Mayasura actually a Danava or a Daitya?"
As per The Brahmanda Purana: Section 3 - Upodghāta-pāda: Chapter 6 - Glorification of The Race of Danu, Maya was a Danava:
4-13. The following are glorified as the prominent members of the family of Danu:—Dvimūrdhan, Śambara, Śaṅkuratha, Vibhu (or lord), Śaṅkukarṇa, Vipāda, Gaviṣṭha, Dundubhi, Ayomukha, Maghavān, Kapila, Vāmana, Maya, Marīci, Asipā, Mahāmāyā, Aśiras, Bhṛśī, Vikṣobha, Suketu, Ketuvīrya, Śatāhvaya, Indrajit, Dvivida, Bhadra, Devajit, Ekacakra, Mahābāhu, the extremely powerful Tāraka, Vaiśvānara, Puloman, Prāpaṇa, Mahāśiras, Svarbhānu, Vṛṣaparvan, Puruṇḍa the great Asura, Dhṛtarāṣṭra, Sūrya, Candramas, Indratāpana, Sūkṣma, Nicandra, Cūrṇanābha, Mahāgiri, Asilomā, Sukeśa, Śaṭha, Mūlakodara, Jambha, Gaganamūrdhan, Kumbhamāna, Mahodaka, Pramada, Adma, Kupatha, Aśvagrīva, the valorous, Vaimṛga, Virūpākṣa, Supatha, Hala, Ahala, Akṣa, Hiraṇmaya, Śatagrīva, and Śambara (the second).
- There were fourteen thousand more, those of the residents of Hiraṇyapura. Paulomas and Kālakeyas were Dānavas of great strength.
28-29. They could not be killed by the Devas. They were slain by Savyasācī (Arjuna). Six children, five sons and a daughter were born of Rambhā and Maya. They were very powerful. The sons were Māyāvin, Dundubhi, Mahiṣa, Kālika and Ajakarṇa. Mandodarī was the daughter.
"Other than their being descended from Diti & Danu, what is the difference between Danavas & Daityas?"
The same chapter says:
- Thus the Asuras, Daityas and Dānavas have been recounted.
The Daityas are remembered as Sutvats (soma drinkers) and **the sons of Danu are remembered as Asutvats (non participants in drinking soma juice).
Apart from this they were from the same broader group Asuras and we find more similarities than differences.
Daityas and Dānavas is used interchangeably sometimes same as how Nagas and Sarpas are used (Difference between Naaga and Sarpa). For example the Rakshasutra mantra states Bali as Danava king though he was a Daitya king (Diti -> Hiranyakashipu -> Prahlada -> Virochana -> Bali):
येन बद्धो बलि राजा दानवेन्द्रो महाबल: |
तेन त्वाम् प्रतिबद्धनामि रक्षे माचल माचल:।