I've got both and I cannot say which one is better. I more like AmigaOS but this is my personal opinion.
Trying to be objective they are just differet but none is better. MorphOS is an AmigaOS clone and AmigaOS 4 is AmigaOS. If you come from AmigaOS 3.9, you will see that in AmigaOS 4 everything still is where it was while MorphOS introduces a lot of new concepts (from a user's point of view). On AmigaOS 4 you can immediately start to work as you always did while on MorphOS you first have to search this and that. If you liked AmigaOS's concepts, probably AmigaOS 4 is fine. If you always thought that some parts should be different, perhaps you like MorphOS more.
Regarding trolls like Tigger, they always tell that MorphOS is done and AmigaOS4 is not. Well, from my subjective opinion AmigaOS 4 pre 3 feels much more "done" than MorphOS 1.4.5. There are many points in MorphOS where you bump against a wall because it either lacks expected features or just is not finished. I cannot help but on AmigaOS 4 I never had such an experience.
Bye,
Thomas
