That would be my advise, to pick up a G4 with the fastest CPU you can get. Granted I have heard happy reports from users running the Mac Mini with the 64Mb of Video Ram, but anything less than that, such as my eMac, will provide you with issues down the road... which is why I plan on making a video of me shooting my eMac while it is on, so I can hopefully transfer my key to a G4. The eMac's screen is too dark, and without JIT, DOSbox and UAE have very limited uses, though a faster processor and external monitor would fix all that, which is exactly why I want a G4. Likewise having only 32Mb of Video RAM, really does limit you to how many programs you can run at one time.
Complaints about my eMac aside, MorphOS has really impressed me like no other Alt OS has, aside of BeOS/Haiku of course. They work the MorphOS team has done is VERY polished and very professional. I do not suffer from random crashes, slow downs, lock ups etc. There are a few things that could use some improvement of course, but over all I really can't complain, I absolutely love it, and am well pleased with the amount of classic Amiga programs that work flawlessly with it, and most, directly out of the box without any additional tweaking at that, though there will be times you'll have to tweak a few things to get certain things working, but that's true of all OS's.
EDIT: And as a side note, JIT should be on the way in the future.