Ensoniq ESQ1 to SD1, if the latter would stay in tune I'd still be using it. After that PSR630 to PSR2000 - for the operating system sound and extra polyphony then 2000 to 3000 due to on board storage meaning no more floppy shuffles. From a functionality viewpoint the 3000 still does everything I need it's a pity the LCD is now completely useless!