Comparing Ultraverve to CJ 16 or Supratek preamps

I have been a very happy owner of the Dehavilland Ultraverve for the last year but like most here I start thinking about some of the other preamps one reads about in the forums here. I don't feel it is lacking in any areas but still I wonder if there is even more magic to be had with something else (strangely I rarely see any Ultraverves for sale and that might mean something in itself).

One is the Conrad Johnson 16 LS (1 or 2 or even the 17) and the other the Supratek preamps. So if anyone has compared any of these two with the Ultraverve I would be interested to read your thoughts on them.