In my experience, the shape and design of the key has more to with the feel than the material it's made of. The Model M has these bold square shaped keys that feel really good to type on (I'm on my blue logo Mini enjoying them right now). The Topre's keys are tapered more from the bottom to the top, which results in a little less accuracy IMO.
Other than that, I have a set of Northgate double molded keys on my MK96, and they do feel so much better than it's original keys, I threw them away. One of the downfalls of the more industrial Northgate keys is the MK96 is now loud enough to get me evicted.
That being said, no key feels more solid than those on the Model M.