Now the potential of ETH is better than ADA, due to the position of ETH is number 2 in the cryptocurrency market. If you want to make a profit in the long run, I think the best choice is spending money for the top cryptos like ETH.
You can't measure the potential of a coin by it's position in the cryptocurrency market.If a coin has big potential it doesn't matter if it's top 1 or top 2 or top 1000 it will gain more value over time.
That being said however,to me ETH is a better deal.Why? Simply because it is more adopted than Cardano overall.