Bitcoins are limited in supply so they are deflationary (increase in value - gain purchasing power) whereas fiat is unlimited and inflationary (you lose purchasing power over time).
-Renegade
This comparision may be true with regard to Bitcoin - but it's not true about crypto currencies in general. New ones keep appearing, and I see no reason why this should stop. The problem with this is exactly the same as with fiat currencies, except worse. As more and more (limitless) currencies, and units come into being, I see no reason that people will say
"but Bitcoin is the best" - so Bitcoin and all other crypto currencies will become "inflationary" (i.e. lose value,
possibly even becoming worthless).
The real question is, "When you have the option to use bitcoins (or any decentralised, open source crypto currency), why would you ever want to use fiat?"
-Renegade
as per my reasoning above, fiat has some sort of control over itself - cryptocurrencies do not.
(I'm not happy about this but as I
said before, I just cant see a way that it can work. Dont mean that way isn't there... we'll see)