You can probably sense that people are reticent to give you a direct answer. The reason is .... a direct answer may mislead you. What kind of Yamaha do you have currently? What do you want this additional keyboard to add to your setup (other than the 88 weighted keys).
We can discuss specific models, but just like with cars, Ford vs. General Motors is a pretty pointless discussion. BTW, my answer is ... Ford. :D
And I will take the Kurz 2600 series over the Korg Triton series, but I would take the Tritons over the SP88X. Have you considered the PC2?