AMD graphics cards were considered the best choice for mining ten years ago because they offered higher performance on popular mining algorithms of that time such as SHA-256, Scrypt, Ethash, Cryptonight, while being noticeably cheaper. Additionally, mining software (miners) usually debuted for AMD graphics cards initially, before Nvidia. This allowed for early exploitation of new cryptocurrencies. However, at present, AMD has lost its leadership in mining to Nvidia as Nvidia graphics cards are more efficient for mining. Miners for new algorithms are primarily released for Nvidia cards first, and then for AMD cards. The only remaining advantage of AMD products is their price, although the cost gap between graphics cards is not as significant as it was ten years ago.
This doesn't mean that AMD products are completely ineffective for mining at present. Especially with the ZLUDA program, owners of Radeon graphics cards can overcome one disadvantage and start mining cryptocurrencies even if there's only miner software available for Nvidia cards.
