Nobody knows yet when ETH will become PoS nor which coin will be profitable.
Due to this two facts, it's hard to predict anything yet, but Nvidia cards usually are better in more algos than AMDs
There are some another coins using Ethash, and we can
speculate that when ETH become PoS, maybe another coin will use the same algo to get this huge hashrate that will be available, this is my theory, but there's no certainty.
Octopus and Kawpow are two algos that Nvidia performs better than AMD
But nothing is easy, most Nvidias cards are now LHR, you will be good to mine another algos, and at the moment you will strugle with ETH
In my calculations, if you buy a card to mine ETH right now, there's some good chances to pay the card in mid of June 2022, this is the date we have "guaranteed" mining of ETH:
https://www.investopedia.com/ethereum-upgrade-delays-difficulty-bomb-5212447To help you even more, buy the cards with better price, closer to MSRP