There are truckloads of reasons to choose bitcoins over cash. A lot....
1.) Far better security: Since Bitcoins are decentralised, only you are responsible for your funds. It is your responsibility to manage it properly and also you are the only you can access your wallet.
2.) Faster transactions: Since Bitcoins are a worldwide universal currency, you have the option to send and receive funds in minutes, if not seconds. You can send to whoever and whenever you want, provided they also have a bitcoin address, wallet and an internet connection.
3.) Anonymity: This is one of the most liked features of bitcoin- its anonymity capability. All you have to know or give someone is your bitcoin address, which is also something that you can change/replace to even further improve security and anonymity.
4.) Investment Opportunities: Bitcoins can be a commodity, not just a currency. Its easy to invest into and it should bring almost guaranteed profit at this stage as it is in its development phase. This should mean an increase in popularity which will cause the value to go higher as a result of supply and demand.
There are many more advantages to this and we will have to wait and see what the future holds for this cryptocurrency.