I have had many keytars, KX-5, AX-7, Alesis Vortex, and the AX-Synth. My favorite (and only one I have left) is the Korg RK-100 S. It is the perfect size, black, and has a built in synth engine. Made of wood, great mini-keys, fast action, two ribbons. Unfortunately, there is no current editing software that supports modern computer OS versions. The original editor from Korg is still on their site, but it was never updated. That is a great looking instrument:
https://www.korg.com/us/products/synthesizers/rk_100s/page_1.php
-dj