G4 iBook: 
As you can see this example of a G4 iBook is running Tiger. It is also in Japanese, and if the Japanese are using an American computer then it’s got to be good.
Introduced in 2003, the G4 iBook replaced the G3 with an even better setup.
First Version:
800mhz/933mhz/1ghz flavors
133mhz BUS
1.12gb Max RAM
Available in 12’ or 14’ screen configurations
Second Version:
The second revisions included a speed bump for the PPC, larger L2 cache, twice the onboard RAM, and faster combo drives.
1/1.2ghz flavors
1.12gb Max RAM
133mhz BUS
12’ and 14’ versions
Third Version:
1.33ghz standard on 14’ models
Fourth Version:
12’ inch got bumped to 1.33ghz
14’ inch got bumped to 1.42ghz
Max RAM bumped to 1.5GB
Airport Extreme and Bluetooth were added as standard features.
My take on G4 iBook:
Still supported by Apple these are still demanding a higher price on the resell market, in the same since, one could be sold at a nice price. Any of the PPC options are going to run tiger nicely, just be sure to have at least 512mb RAM. I suggest the G4 iBook over the G3 if the price is in your range.
Final Score: 8/10
The G4 iBook is still supported by Apple and still a contender. With airport and tiger you are set to Mac on the go in style. Second revision and later should play nice with leopard.
G4 PowerBook: 
The end of the line in the legendary PowerBook line, the G4 model came in a s3xy brushed metal case. There were a lot of configurations released all the way from 400mhz to 1.67ghz. Make no mistake this is the predecessor to the MacBook Pro.
First version:
400/500mhz
100mhz BUS
1gb Max RAM
15’ screen
*I would avoid getting a first version since it has no real performance edge over a G4 iBook and the iBook can be found cheaper.
Second Version:
Inclusion of Gigabit Ethernet Port
550/667mhz flavors
100mhz BUS for 550/ 133mhz for 667
Airport standard for 667mhz option
Third Version:
800mhz added as a PPC option
133mhz BUS now standard
Fourth Version:
1ghz option available
First laptop with a slot loading “super-drive” (DVD-ROM/CD-RW)
Fifth Version:
12’ inch version made available with 867mhz PPC.
32mb NVIDIA GeForce4 420 go Graphics
Basically a styling alternative to the white iBook, even though these PowerBook versions are slightly smaller in size than their cousins.
Sixth Version:
17’ inch version was the largest laptop screen configuration available ever at the time.
1ghz PPC
BUS speed boosted to 167mhz
Max RAM boosted to 2gb
Seventh version:
12’ model with added mini DVI port as well as USB upgraded to 2.0
1ghz PPC
1.25gb Max RAM
Eighth version:
15’ version with Firewire 800 ports added
1 and 1.25ghz versions
2gb Max RAM
High-end version featured standard airport extreme, super-drive, and self-illuminating keyboard.
Ninth Version:
PPC Bump to 1.33ghz for 17’ model
Tenth Version:
PPC Bump to 1.33ghz for 12’ model
Eleventh Version:
PPC Bump to 1.5ghz for 17’ model
All PowerBooks come standard with Airport extreme from this point forward.
Twelfth version:
PPC Bump to 1.5ghz for 12’
Thirteenth version:
15’ version gets a 1.67ghz PPC option
Max RAM bumped to 2GB
Fourteenth version:
17’ gets PPC bump to 1.67ghz
Fifteenth version:
Last models to ever bare the PowerBook name
15’ and 17’ models get dual layer Super-Drives and faster RAM.
Higher resolutions supported
No PPC Bump
My take on G4 PowerBooks:
These are great machines, however can be pricy on the aftermarket. Second versions and later are better to run tiger with. Since these are the predecessors to the Macbook Pro, you will find people trying to pawn them off at prices that may be a little steep; so that they can have more cash towards a Macbook Pro purchase. The aluminum cases on these make for nice aesthetics. If you are looking for something a little more than an iBook, but don’t want to pay the price of an Intel; these may be for you.
Final Score: 8.5/10
Better performers than the iBook but they don’t come as cheap. In my opinion they look better than an iBook and are a little sturdier. Due to current EBay prices being high, they don’t get a full point over the iBook. However, if you have got the cash then definitely go with a PowerBook over an iBook. The 1.33ghz models with Max RAM will provide you a Mac on the go that will be useable for quite sometime to come.