wico: Enclosed case, bigger than happs. Rollers located on top and left sides
probably better for flat control panels and/or golf & bowling games. Mounting holes a fraction too small for use with happs mounting kit (
http://happcontrols.com/trackballs/55110100.htm) without redrilling them a little bigger. Smooth roll, but doesn't free spin as long as the happs 3" high lip. 1/16" lip
happs 3" high lip: Encoder wheels exposed. Smaller case than wico. Rollers located on bottom and right
probably better for tilted control panels and mostly downward spin games (marble madness). Took a little longer to break in, but still is a little "louder" than the wico. Free spins longer than wico. 3/8" lip.
Both are nice arcade quality trackballs. Both work great with optipac. Same wire layout, same location mounting holes. I said "probably better" above because of physical layout, but didn't really notice much difference in use.
I've talked about the differences in prior threads, too. I went into a little more depth those times, but, basically, you should be happy with the wico under most conditions.