Well it would be for sheet music, so ideally it would be in the 6"+ range. The bigger the better. Really just depends on cost - I don't want to spend more than a couple hundred bucks (otherwise I would just buy the PadMu 2)
Could I get more info on the "wHAT"? I tried googling for it, but there are a ton of false positives (due to "wHAT" being the same word as "what").