Have you seen those new Mackie mixers that use the IPad as the brains? Kind of cool. The guy who did our sound in Vegas had one and he could walk all over the room and check the sound/mix etc.
If it was me, I'd get the smaller one. I have an IPad 2. Gathers dust except for travel and sometimes using V Control Pro - which makes pro tools sort of like the Mackie setup - you can mix from anywhere. But I don't use it all that much anymore.
for travel they're great. Metronomes, tuners, portable recorder. Kinda cool.