Between the Korg and and the Ketron. I personally would take the Korg. It has a better screen (color and touch), The controls on the Korg seem more logical to me. The pitchbend and modulation are to your left on the Korg rather than up and to your left on the Ketron. Sounds are subjective with both models.

As far as the Kurzweil and the Triton. That's a good toss up there. In the sound department as far as acoustic instruments are concerned I think the Kurzweil has the edge there. You also have to consider the poly issue with the Kurzweil too. I think they say it's (true) 48 poly (whatever that means), and the Korg has I think 128 (pretty sure that's what it is or close). Both of those models have their good and weak points. You may also want to consider the Yamaha Motif series and the new Roland Fantom series. Those are both great synths too.

Squeak