not a smart ass reply: the best one you can afford.

if you're looking at laptops, don't do the ibook. the processors may be similar but the cache, ports and a few other key things are not the same. you'll want a pb if you're going laptop.

desktop, there are more choices. G4s are still plenty-to-very capable. If you do some homework, you can even buy one a few years old and upgrade the processor to something kick ass for less than you can buy a new machine with lesser specs. eshop.macsales.com and xlr8yourmac.com are good places to investigate upgrade issues.

that being said, a G5 is naturally still more powerful and a bit more future proof, depending on your needs.