I use Quick Book online, it can be used with a lap top, a tablet, and your phone. The internet based version is more detailed then the app as far as capabilities, but you can just log in to the internet version off your tablet or phone if you have to. You can add customers, create invoices, estimates, and receive payments with the app. You can even have the customer sign an invoice on the tablet. I use the pro version so I can enter bills and pay them through QB.
The Software version is definitely offers more functionality, but the online version is better suited for a mobile office.