It would be nice to see the 6 grid version from @SteveJordanKW’s designs in @wenples Sketch 8/9/10. I think I prefer the unique color blocks instead of some singles and some duplicates. Something about the two green, two orange but one blue, one red doesn’t seem as nice though I get it’s probably trying to be symmetric.
The extra spacing between “3D” and “Slicer” from what is in the current logo should be done. I think it would be nice to use the primary color from the logo mark as the text color for at least “3D” but maybe all of “3D Slicer”.
I’m not much of a fan of the purple shade with the gradient. I think a grey is more recognizable as a Slicer brand and more similar to the current logo.
I think I still prefer @SteveJordanKW version C design as it just looks more modern with the flatter design more prominent in recent OS versions while heavy shading was more prominent of an OS from 10 years ago. I think a few extra flat shades can help provide more depth to emphasize the 3D aspect.