Turns out the competitor to the Radeon RX 6600 (in mining) is the smallest Ampere workstation GPU, the RTX A2000. Tests conducted by Dizzy Mining show that the A2000 is even more efficient than the RX 6600
Nvidia’s new Ampere-based pro GPUs are great mining cards, the Nvidia RTX A4000 and RTX A5000, offer a big step up from the Turing-based Quadro RTX family. With more memory and significantly enhanced processing, these cards are vey power efficient for mining but may take a hit on the re-sale value.
The Radeon RX 580 4gb can’t mine Ethereum anymore due to the DAG size, but it can still get a decent hashrate on RVN and other algorithms with a Bios mod. These cards also have a very fast ROI if you can get them at the right price.
The Radeon 6900 XT is a high-end AMD graphics card with the highest efficiency in the series. This has now been surpassed by the 6600 and 6600xt. It was released in December 2020, three weeks after the RX 6800.