I have used the CV 21/4, but sold it because it just seemed "character-less". I have used the Kobalux and it was great. I SHOULD NOT HAVE sold that one, but did, to a buy a 21mm F3.4 Super Angulon, which has a lot of "character" (perhaps too much sometimes).
In retrospect I should have stuck with the 21mm Kobalux as a good all around 21mm, it's much larger than the Super Angulon, but also a good stop faster.
For the last few years I've been happy with the Super Angulon. 21mm is not a focal length I use that often, so having a small lens that normally lives in the bag is important to me. The Kobalux was a tad too large for this, plus it took big filters (58mm diameter if I remember correctly).