Bitcoin has a limited supply. Meaning when people lose their private keys the supply will be actually decreasing meaning that it's a deflationary currency which is not good for buying selling stuff because if you hold it gains value
It more like digital gold, an investment that holds and increases in value over time.
Ethereum has much higher chance to become the future currency. If most of the services will be built on top of Ethereum and people will use ETH to pay for those services, that would make sense.
In my opinion none of the above will be used as a currency, we need a stable coin that will keep the same value. I think the best one until now is
Maker.