Depends on what you're after.
BOth Alesis Ion and Korg MS2000 are good for analog emulations and other kind of purely synthetic sounds.
If that's all you need then I suggest you go for them.
If on the other hand you need sounnds like pianos , strings, organs, rhodes and some synth stuff as wel you'll be better off with something like the JUNO D which isn't really much of a synth when it comes down to analog sounds and synth textures but it has a little bit of everything so therefore it might be more useful to you.
-ED-
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A gentleman is one who never hurts anyone's feelings unintentionally.
- - - Oscar Wilde