Whoa!! Korg and Ketron are vastly more expensive than an entry level Yamaha. I would suggest learning on a real piano. Barring that, a semi-weighted board with at least 5 octaves. Built in speakers are great too but not a necessity as you can always use headphones (a good idea if your a beginner). Don’t base your desicion on sound quality or accuracy. When the student is far along you can always upgrade to a higher quality instrument. Try the NP-31 from Yamaha. It runs close to $300. Try not to get mixed up with the One-man-band machines. They are a different animal.
