There are many calculators online that you can use to know which GPU is most profitable nowadays.
Based on my experienced If I compared them both AMD GPUs vs Nvidia GPUs these days Nvidia is mostly more profitable to buy due to more mining software release and more Algo for Nvidia cards.
Look at the grin coin or beam coin if you want to mine this coin you can't mine them with 4gb GPU ram they mostly use gtx 1070 and gtx 1080ti.
So I suggest you choose GTX 1080ti so that you can mine with other coins compared to rx470.
However, some calculator will show you that x3 rx470 is way more profitable than gtx 1080ti but the problem you can't mine on other algo and mine new coins.
You can also try this one
https://www.nicehash.com/profitability-calculator for calculation but I don't recommend this software to mine and auto exchange all of your coins into bitcoin.
Holding coins is better than selling them while the coins still not profitable.