Why some people prefer Bitcoin over fiat ?
so its because transaction in Bitcoins occurs instantly, You pay a very small amount of fee for any transaction, Bitcoin rates against fiat currencies worldwide fluctuates a lot and the profits (and losses) could be very dramatic very soon, Bitcoin Network is Secure, Bitcoin transactions are anonymous. so the reasons behind ppl prefer bitcoin over fiat is security, fast transaction and universal nature.
I think when it comes to transaction time, bitcoin is actually slower. Unless you are willing to pay higher transaction fees, then your transaction is more likely going to take a couple of hours before it gets confirmed. Basically just think of it, as the transaction fee increases in bitcoin, the transaction time becomes lower. The transaction fee is high by default when transacting in fiat but the transaction time is really low. I think it's the same when it comes to that aspect. If you're willing to wait, just select bitcoin since it has cheap rate.
Along with all the obvious reasons (anonymity, cheap tx fee, security, etc) I choose bitcoin because the people that are selling digital goods on the Internet are only accepting bitcoins. Some in my place are also accepting load rebate but I think that's just a lot less convenient than having only one platform to transact with everyone on the Internet. Plus, the transaction fee is not as low.