I've used both for film and digital. Both are, as already mentioned, so good that we wander into "lens character" discussion... and that's good, but... for me(and an M8) the coding was the issue, so I sold the ZM25(and kept the ZM28, btw). The ZM25 is a tad more neutral with color, but in B&W, both have great tone. Wide open, the ZM25 is a bit more "consistant" across the frame; however, this "consistancy" stopped down renders images a bit, um, "consistant"/predictable/clean/flat. I prefer the L24 rendering, and am lucky to have one to use... that's the other issue: getting one, and at near the cost of the ZM25. Happened to me, could happen to you!
I've quite a few ZM25 images that inspire... does live up to the praise.
As for the CV25... I shoot an older LTM Skopar too... but when the scene gets complex(read: includes more human created forms and less of Mother Earth, like architecture), the distortion creeps in. Color like the ZM25, but this lens is much more "expressive", rather than descriptive(as the ZM and Leica do famously).
So, you're shooting film, now. Both cost a wee bit... have you considered whether you'd "Go Digital"(TM)? If not, or for a while, I'd recommend the ZM25. And of course, if you can choose between the two, and cost is +/- 100 Euro... Leica 24 would be my suggestion.
rgds,
Dave