What is the Best Mac for playing old games ?

As I said, Mactracker is your "bestest" friend in this. You can research this yourself.

The last G4 that could natively boot into OS9 was a special run of 1.25ghz single-processor models that Apple released in 2003 and 2004 in demand from graphics designers who still used Quark Express for layout. Quark was dreadfully behind in devoping OSX versions and their OS9 version would not work properly under Classic emulation. Apple threw the graphics community a lifeline.

However, shopping for one of those G4s is risky for a couple of reasons:

1) There is nothing obvious about the computer that screams "I am OS9 bootable!" You may be able to tell from the serial number and a number-to-model conversion website ( ex: http://www.everymac.com/ultimate-mac-lookup/ ), but the Machine Model/Model Identifier code in System Profiler and the Model Number on the ID tag are the same as those that are NOT OS9 bootable. That is why you really need Mactracker: it shows order numbers and codes that may help you find the right machine.

2) Even if you find the proper 2003 G4, if you do not get the ORIGINAL-TO-THAT-MACHINE optical disks, you cannot install a bootable version of OS9. To get around the prior eviction of OS9 from their computers Apple had to come up with a special version for just that model. No other disks will work.

Mactracker shows the order numbers for models that support OS9 booting. There was an earlier DP 1.25 that is allegedly OS9 bootable. Here is the MacTracker listing for earlier MDD models that are supposed to be OS9 bootable, with the ORDER number section highlighted:

The order number for the special 2003 1.25G SP version was M9145LL/A.

Don't waste too much sweat holding out for a dual processor. Many of the games from that time are not DP-aware.

It appears the 1.25ghz G4 iMacs would not natively boot into OS9; they can only use the Classic emulator which is poor for gaming.

An idea of old games you are considering may help us. Some do well with minimal graphics hardware and other need the power of a PCI or AGP video card. I did a lot of flight sims on pre-Intel Macs (mostly a Beige G3 heavily upgraded) and they can require massive video hardware for best function. Some were very card-specific. I had an F-16 Falcon sim that ran fine on an older 16MB ATI video card that would not work for beans on a newer and more capable card from ATI. It was like the sim was hard-programmed only for certain cards.

Also a PowerPC Mac that natively boots into OS9 is far preferable to having to run OS9 via the Classic emulator. Later G4 MDD models can only run OS9 via Classic. I believe the G4 you mention would be far better than any G3 tower or the G4 iMac.

I recommend you consider getting the free database MacTracker. It shows the OS versions originally shipped on every Mac model so you can tell if a model is natively bootable into OS9. MacTracker is in the Mac App Store here:

https://itunes.apple.com/us/app/mactracker/id430255202?mt=12

or from the developer's site here:

http://mactracker.ca/

You also may be interested in...

http://www.cultofmac.com/251814/still-miss-your-old-macintosh-run-mac-os-7-in-yo ur-web-browser/

http://www.cultofmac.com/259844/openemu-ultimate-old-school-game-emulator-os-x/

I've had fairly good success with SheepShaver in OSX/Intel.

http://www.everymac.com/systems/apple/powermac_g4/specs/powermac_g4_1.25_mdd.htm l

http://www.everymac.com/systems/apple/powermac_g4/specs/powermac_g4_1.25_dp_mdd. html

But not the FW/800 model...

http://www.everymac.com/systems/apple/powermac_g4/specs/powermac_g4_1.25_dp_mdd_ fw800.html