my 0.2:
AmigaOS4.0 does not exist for end users.
MorphOS1.3 exists for "advanced users".
AmigaOS3.9 is the most complete existing Amiga(like) OS release.
AOS3.9 vs MOS1.3:
AOS is more complete while MOS is a lot faster because it is in native PPC code. And MOS have some unigue extra features when compared to AOS3.9.
If PPC native AOS4 will contain all AOS3.9 bits and pieces + something new when it's released, it should be a winner.... IF it is released soon... U C MOS is not standing still.