If you're looking for a late PPC Mac to run esoteric PPC operating systems or PPC Mac stuff, the MDD G4 is a great machine if you need dual processors, expandability, and more than 1 GB of RAM.
But if you don't, you're much better off getting a Mac mini G4. I'm biased because I have a hobby business selling SSD upgraded ones running a hacked Mac OS 9 [0]. But compared to the MDD G4, the Mac mini G4:
- Uses a fraction of the energy
- Takes up a fraction of the space
- Largely can run the same operating systems
- Is much quieter (as the article alludes to, the MDD G4 is loud)
- For single core can actually be faster going all the way up to 1.5 GHz (MDD can go there with an accelerator)
- Has more integrated parts so has less parts that can fail
There are some cons to the G4 mini versus the MDD G4 though:
- Almost no expandability
- Limited to 1 GB of RAM
- No dual processors
- The hacked version of Mac OS 9 needs USB sound and some models can have some display incompatibilities at high resolutions
But for the vast majority of applications these don't matter much.
I'd say the best PPC Mac will depend on exactly what you want to do on it.
Fastest that can natively run OS 9 with full driver support is going to be the MDD.
Best low cost and low space for tinkering is going to be the mini with the caveats you mentioned.
Best price to performance on the used market for PPC OS X software is probably an iMac G5.
Absolute best performance for PPC OS X stuff is going to be the PowerMac G5.
Honorable mention to the eMac, which can be be found for ~$100, 1ghz combo drive models and below can natively run OS 9 with full driver support or you can go with up to the 1.42 ghz model which is going to be similar to the fastest G4 minis, and comes with a beautiful built in CRT, with the caveat that it takes up as much space as a CRT.
Any plans on doing a PowerBook edition?
No, it's just a hobby and I'm way too far into this niche having purchased the particular parts for the mini G4 in bulk. Plus there is the built-in know-how of having done nearly 100 of these refurbishments/upgrades that I don't have the time to build up for another model.