ion 12, what kind of music do You want to make? The MS2000 is not a synth for everything, it can't emulate natural instruments. But it sounds nice and is more or less easy to program. But it only has four voices. The RS-5 can emulate nearly every instrument, has 64 voices but isn't easy to program.
If You don't need a sequencer I would choose a Roland XP-30, if a sequencer is needed a XP60 or 80. But You'll need to buy them second hand, because otherwise they'll be too expensive.
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Nils