XMR is probably your best bet for privacy digital currency.

That said XMR isn't stable like the USD is, but it also didn't have infinite printability as once market cap is reached then only tail emmisions are rewarded for mining....iirc that a set value of 20.

XMR is the best for privacy, is resistant to asic mining and GPU mining, and is a time proven crypto. That said if your just using it so you can gain money from price fluctuations and not because of the fiction the coin provides then your never going to realise it's true value.