It's a good idea to save in bitcoin but then bitcoin is volatile in short term so the risk is quiet high in short term but if considering long term then bitcoin is best choice Viz vice with fiat fiat is best option for short term because it's leads volatile in short term so saving in fiat for just a little amount of time is good.
I think the main advantage of Fiat is that it is easy to spend it, that's it.
It is hard to sell an investment to pay for a coffee, but with fiat you don't have that issue.
It's the same with bitcoin. Unless you use lightning, then it is not as simple to do transactions. But that's fine, because you can store your savings in bitcoin and spend with lightning, or Fiat if you need to.
The key is to save in bitcoin instead of fiat.