Any of those you list should work well. I have a Roland A-33, which is an older model (I don't know what the modern equivalent is or a value).
I'd be scared of an old Casio, Medelli or Technics - the backup on those is shaky when they are brand new, so I can only imagine what it's like with an older unit. The Casios in particular are known for flakey MIDI implementation, so might not be a good idea if you want to use it as a controller.
Sound wise, I doubt I'd want to tinker with the sound much (I believe that's what a synth does?), I'd like to be set up in a way that I just pick an instrument and play, I take it that's what a sample library is?
Strictly speaking, a synth generates the sound electronically from scratch. A sampler uses samples - recorded snippets of the real instrument it is copying. Consequently, a sampled sound is usually more natural, while a synthesized sound is more electronic. A sample library is just a collection of sound samples.
Most of the home keyboards and pianos use sampled sounds. Softsynths like the Roland Sound Canvas or Native Instruments Bandstand use samples too. A controller (once again, strictly speaking) has no sounds of it's own, bu rather just sends the MIDI note messages for a synth or sampler to play.
BTW. What software recorder are you using? Does it have softsynths built in?