Which one? (Powermac G5 or Powerbook G4)

Get both, since either machines are cheap these days.

 

Any G5 is going to be as good as even the fastest G4 PowerBooks. I really do love my PowerBooks, but the RAM capacity really is a barrier that is hard to avoid. Aluminum 15" and 17" PowerBooks cap out at 2GB of RAM which really doesn't give you a ton of space to work with. That said, they are still very nice computers and if you get one thats 1.5GHz or better, you really can use it as an everyday machine IMO. What are you willing to spend? If you can give us a ballpark, it'll be easier to suggest what the best system is you can get your hands on.

 

I went through a similar dilemma, I went for portability over power in the end though. But your circumstances may/probably will be different.

If you're looking at the G5's, at least get a dual 1.8, you can get these seriously cheap now, 125 gbp (190 USD), and for the love of Macs, stay away from the liquid cooled ones...

If you're looking at the PowerBooks, but want for example, AS CLOSE speeds to the G5 you'll have to get either the 1.5 or 1.67. You can get a 15" 1.5 for around the same price as the G5's.

But as lgwells said, if you have the money, get both! They're both awsome machines in my opinion and then you've got one workhorse for the desk and a little rocket for a portable!

 

Go for a top of the line MDD G4 like I have. See my sig.

With a dual G4, you'd get more performance than a PowerBook, and still be close to lower-end G5s. The G5 is notorious for failure and i highly do not recommend getting one.

 

A G5 will totally smush the PB performance wise, decent Powerbooks are nearly at the price of a Macbook anyway. Although for your purposes, developing, I'd say go for the Power Mac.

 

Get either a High End PowerMac G4 MDD or a G5. While the PowerBook is great for development (Before I jumped to Intel my main development machine was a 1.67 PowerBook G4), a PowerMac is much better as its faster, more expandable and lets you use more displays (a real boon for software development). It also doesn't have the 2GB RAM Limit which can be rather pesky. Ideally for PowerPC Development you'd have both a laptop and desktop. (I still develop for the PowerPC Platform as a hobby and I use my 1.67 PowerBook G4 and my PowerMac G4 (and when its not on loan, my G5) as development machines - and both have their uses).

If you do get a G5 make sure you get one running at or below 2.3Ghz, as anything faster than this will be water-cooled and these are pretty much guaranteed to eventually fail and leak lovely corrosive coolant everywhere.

 

In your case I would recommend getting a desktop Mac. Especially as if you need Mobile Development you have a MacBook (depending on which version of OS X and Xcode you have it may be able to target PowerPC). It then becomes a choice between the G4 and G5. For your usage it sounds as if RAM capacity would be a plus, in which case Id do more research and find a stable (< 2.3Ghz) G5.