Of the ones I've owned, it must be Ketron SD1, because that's what I'm playing now.
I also enjoyed the Tyros a lot.
The keyboard that was WAY ahead of its time was Technics KN2000, but of course it's history now.
Another such "precocious" keyboard was Yamaha PSR8000, the first to have a really workable vocal processor and harmonizer.
Can't compare the latest Korg, Roland or GEM because they aren't available to me to audition. Also, the weight keeps me from seriously considering them.
DonM
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DonM