1) AmigaOS 4 will use Reaction as a core GUI interface, and MorphOS will use MUI.
- I don't know what the latest version of Reaction is like architecturally, but I know that MUI is praised for its architecture, even if it is a bit more resource heavy. With PowerPC machines this isn't a problem, so probably a win for MUI, pending more information on Reaction. Then again, as long as they do the job and provide a full set of widgets and layout features who cares?
2) AmigaOS4 has native PowerPC TCP/IP stack
3) MorphOS currently has a prettier icon system
4) Both have themeable and configurable interfaces
5) AmigaOS4 is stuck with Workbench without many improvements until the new version is written. MorphOS has Ambient, which although I haven't used it, may have more modern features. Certainly icons, et al, aren't that hot on AmigaOS4 at the moment, although not terrible.
6) They both are a long way away from what a well funded OS team like Apple's can create.