If already you picked up a Mac to potentially run MOS, I would go that route and save for the OS in the meantime.
MOS has the best feeling of what Amiga OS is. It is extremely fast, consistently evolved over many point releases, runs many 68k applications, and is the most polished over any other offering. Feelings are emotions and therefore subjective, but to me MOS feels the most like Amiga. To be fair I haven't personally used OS 4, but from the videos and comments it seems that it has a real flavor of 3.x 68k. If you want love the classic Amiga feeling that would be your choice. The entry price for OS4 on the latest HW isn't cheap though...
Good luck.
