I can't really tell you what's better but if you like Yamaha then the choice propably is...the Fantom??? Isn't it a synth made by Roland?

Otherwise if you're using so much synths by Yamaha then a new sound colour made by Korg could be amazing. But at the end you will have to decide it for your own. Like Bluezplayer said try to figure it out! You have your own key feeling and your own imagination of that what should come out of it...

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Greetings from Frankfurt (Germany),
Sheriff ;-)