Just to throw my 10c worth into the conversation,I have recently purchased an iconnectaudio4 interface. This allows me to connect and charge my ipad and iphone at the same time, with 4 audio inputs, 4 outputs (+ phones) and multiple midi options (DIN, usb)
This means I can route audio (guitars, keys, bass, vocals) through either I device, through bias fx, loopy, or any other app, as well as controlling midi apps (animoog, sample tank etc)
Takes a little setting up and getting used to, but the possibilities are endless