Bitcoin advantages are:
Decentralized
Storing money outside banks
Sending money in a matter of seconds
Really small fees
Great currency for online payments
Blockchain that can be used for various purposes
Fiat advantages are:
Acceptance everywhere in the world.
Best payment tool in the offline market
Maybe you're forgetting about this fiat is having a legalization from government and the value of fiat is always permanently. but I think it's very irrelevant to comparing fiat with BTC and fiat and BTC is made with different interest.