Personally I would choose OS/2 over Win3.1 anytime. OS/2 was more "Mac like", for example, properties and preferences dialogs did not have the Apply/Cancel buttons, you had a Default button to reset to factory settings or you could simply close the dialog for your changes to be applied.

This said, I believe that what made a big difference in look and feel when Windows 95 was released was the introduction of TrueType fonts that had much better rendering. OS/2 was using PostScript fonts, and introduced support for TrueType much later... If I remember correctly thanks to the open source efforts of the FreeType project.