Difficult comparison when you through the J12 in, as results vary greatly lens to lens. Its a solid performer but I found them to flare very easily without a hood. I had better luck with J12s on Kiev bodies than on LTM bodies.
I just never connected with the Olympus XA. I really wanted to like it for some reason the results I got out of the lens just didn't make me happy. I felt like the image quality was lower than with other cameras I was using but could never quantify it. Maybe I had a bad copy of the camera? I'll probably give it a go again at some point. If you want something compact though, this definitely is the winner.
The Yashica 35CC is great. Love mine with one little exception - the aperture blades result in weird, distracting bokeh at times. It isn't an issue in most of my shots though that would depend on shooting style and subject. Great lens. Much more of a regular camera feel than the XA.