We have an older kayak erg that works about as well as you could hope to simulate paddling. Some of that simulation is in your hands (and legs and core) since you have to focus on feeling like you're pushing instead of pulling in order to get it right.
When we want a high end paddling product, we get advice from Mike or Dav Fekete of Kayaksport Canada who sold us our erg, surfski, paddles, etc. It looks like PaddleOne is the only erg they sell now and that alone makes me think it must be great. Seriously, they are picky.
http://www.kayaksport.net/products/machine.html