The best advice any of us can give you is to sit down and play each of those you've listed. As for the Casio, to my ears the styles were good to excellent, lots of things that I would never use though, but the voices were marginal at best when compared to the PSR-2100--not even close. The 8000 is also a good machine, but I still prefer the versatility and portability of the 2100, which weighs considerably less.

Good luck on whatever you decide upon,

Gary