I've always found 25 to be too inbetween a focal length for me--of course choice of focal length is so subjective; however, I find that a 21 and 28 are a good combination. I sold my 25 and don't miss it. I have the CV 28 and it is great (sharp, even tone although some vignetting at wider apertures)--very contrasty though, so depending on your taste... I understand the canon 28 by comparison has less contrast--I think Winogrand used the canon extensively--might be a good place to get a feel for the lens.
-Barry