Is there a particular form factor people prefer for SmartGo on iPad? I don't know, for example, if it lays out differently on a mini vs. an iPad Air or whether a Retina display makes it look better or not. Does anyone find input or use of SmartGo books more awkward on a mini?

I'm kind of leaning toward the larger form factor just because I have older eyes, but would like to know if there are other considerations I should be aware of...

I've hand an 1 and an Air (so, non-retina and retina) and both work well. But now that I'm used to the retina-ed... I wouldn't think of using the other one. The new iPad mini also has retina, so the non-retina models are at least one iteration behind.

The iPad may be a little large and heavy for casual reading, though.

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i use an ipad mini, much easier to put on a table for recording games
and easier to hand hold if you're reviewing games up on a demo board

Use cases worth considering, though I have some aversion to electronic recording.

i used to do pen and paper with my own kifu that i made (and subsequently entered into an sgf later)

i prefer using the ipad mini (in fact it's all i use the ipad mini for really)

ipad mini is smaller, lighter, and cheaper with no real slouch for power compared to the ipad
the screen size being smaller isn't really an issue for recording either
i also downloaded a copy onto my iphone in the cases where i forget to bring the ipad to go club.

being able to fit a regular ipad onto a table in a tournament with people around you might be harder with the constraints compared to an ipad mini. which is another reason i like it