If you are thinking that Korg has better sounds, I would strongly recommend that you listen to it, as well as to Yamaha.
Sound is a very subjective thing, but to me Korg sound has always had a harsher, edgier tone - fine for playing techno/electronic dance music, but not so good in reproducing real, acoustic instrument sounds, which is what most of the arranger players seek. This has been true for Korg sounds across the board - from their earliest arrangers i3, i30, up to the newest PA series (and also Triton, which they tout as a "flagship workstation").
Roland has the warmest, mellowest sound - I like it the most, but some people do not. I believe Yamaha sounds are somewhere in the middle, between Korg and Roland, which is why most people like them.
Sound notwithstanding, Yamaha is a much easier to use instrument. Korg's dual sequencer is a pure gimmick on the PA50 - it has no hard disk for mass storage of the MIDI files. PSR3000 has a USB connection allowing you to connect a USB mass storage device, such as thumb drive or a hard disk. Plus it has a vocal harmonizer, which Korg does not have.
I'd say go with the Yamaha, but if you can, listen to the others first.
Regards
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Regards,
Alex