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Consider four key factors: memory size (how much data you need to store), security requirements (password protection vs AES encryption), read range (how close the user needs to be), and cost per unit at your expected volume. For simple URL tags, NTAG213 is the most cost-effective. For product authentication, NTAG 424 DNA offers secure dynamic URLs. For multi-application smart cards, MIFARE DESFire EV3 provides the highest security.

Most NFC Forum-compliant chips (NTAG 21x, MIFARE Ultralight, DESFire) work with both platforms. Android has supported NFC since version 4.0 (2011). iPhones support NFC tag reading from iPhone 7 (iOS 11) with background reading from iPhone XS (iOS 12). NFC tag writing requires iPhone 7 or later with iOS 13+. Check the compatibility section on each chip page for specific iOS version requirements.

Total memory is the full EEPROM capacity of the NFC chip, including internal configuration bytes, capability containers, lock bits, and manufacturer data. User memory is the portion available for your NDEF records (URLs, text, vCards). For example, NTAG213 has 180 bytes total but only 144 bytes of user-accessible NDEF storage.

Most NFC chips guarantee data retention of 10 years or more, with many specifying 25-50 years under normal conditions. The EEPROM technology used in NFC chips does not require power to retain data. Write endurance is typically 10,000 to 100,000 cycles, meaning you can rewrite the tag thousands of times before the memory cells degrade.

It depends on the chip's security features. Basic tags (NTAG 213/215/216) can be read and duplicated onto blank tags, though the UID is unique and read-only. Chips with originality signatures (NTAG 21x) allow verification of genuine NXP silicon. Advanced chips like NTAG 424 DNA and DESFire EV3 use AES-128 mutual authentication, making cloning computationally infeasible.