I had to think about this as I mostly played sax, or guitar
in my earlier years. But I remember that my first keyboard was
a Farfsa Fast 3 organ. After that some of my personal other keyboards
through the years have included (not necessarily in chronological order)
Halifax Duo organ
Hammond BC organ
Hammond M100, Univox Elec Piano
Hammond B3 , Rhodes 73, Arp Strings, Moog Satellite
Yamaha CP30 elec piano, Moog Rogue, ARP Omni
Yamaha CP70 Piano, Korg CX3, Moog Opus 3 ,
Yamaha SY55, DX7
Ensoniq Mirage, ESQ1, SQ80, KT88
E-mu Emulator lV, E-mu Esynth
For me, the B3 was the most inspirational to my playing. These days
I use NI B4ll.
I've never owned a Casio though.