You cannot outrightly use crypto cause mainstream adoption is yet to be achieved, thus even if you're a crypto user/enthusiast, you'd still have to use fiat for your everyday needs, maybe when crypto goes mainstream and you can pay for practically everything with crypto, then people can decide which of the two they would actually prefer to use, but atm, it's either you're a crypto user, using both, or you're anti-crypto and you're using just fiat.

Having said that, on the coin of my choice, it's definitely going to be Bitcoin, it is sustainable for the long period and it indeed has a worthy use case, altcoins are more or less short term investments and too many of them are pump and dump coins, I believe in just the Bitcoin network and a little in the ethereum ecosystem, thus i would just stick with Bitcoin and if I want to invest in altcoins, then ethereum.