I have noticed variability in the feel of several of the pioneers that I have (HP32sii and 42s). While normally the tactile response is good, 2 machines that I bought off ebay had keys that felt slightly spongy. The ones I purchased new have seen lots of use, and the tactile response is good. The ones I got from ebay were stated to have not been used much for a long time.
If a pioneer sits dormant for a period of years, is it likely that the keys can go spongy? I have an 11c that has sat dormant for years and the key action is still excellent.
My vote for best keys has to go to the voyager series.