The nerds I have talked to say BTC has some unique advantages, #1 being it was first to market and has major brand recognition.
Other than that it has a defined, finite supply. So while you can argue over whether it’s worth jack as an actual currency, it’s also an attractive and obvious option to replace gold as a worldwide, fixed standard of worth and a solid hedge against inflation.
Ethereum is attractive due to its functionality I think, but I also have no reason to believe it wouldn’t co-exist with BTC. Other coins could serve niche purposes too.
Dogecoin as far as I can tell is just a prime example of what unregulated markets can give you.