Micro Korg is OK. If you need more than 37 or so keys get a used DX7 - it's affordable as well as rock-solid and will last you for a long time (it's almost bullet-proof). But to get the full use out the DX7 as a controller get an "SER-7" update (contact Yamaha abot that). It doesn't cost much.
Let me know if you want more info or other options. I'd go with the DX though. I had one since I was a kid (for 15 years now!). It still works - NOT even a SCRATCH on it (although it's been through a lot) Great aftertouch too.
Ivan.
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A gentleman is one who never hurts anyone's feelings unintentionally.
- - - Oscar Wilde