perhaps bluetooth?
Most important is plug and play on any computer without user action like installing drivers, if it can be done with bluetooth, why not, but USB has every computer and bluetooth only some computers.
The most important function is security though
agreed,bluetooth might not on every computer,but i think bluetooth have good function for private file transafer,imagine if we can share file from bluetooth without switch internet connection on. yes i agree,the most important is security function,but also the price will matter for some people,its must be equal with security,good price should mean good security.