Depends a little on what you want to be doing with your system
The A600 won't bring much more then what you already have.
Apart from PCMCIA harddisk and perhaps some acceleration the machine is pretty limited.
The A1200 is probably the best. Accelerators are easy to find. You could start off slow with just a ram expansion. The machine allows anything the A600 does with a little extra kick. You can even go beyond sanity by building a tower and adding a busboard and all kinds of wicked expansions like voodoo card, sound card ....I dont really know much about this level of expansion. I prefer original cases.
Putting software on either A600 or 1200 is no problem because you can add compact flash and exchange files with your PC.
The A4000 can be turned into a monster aswell. However accelerators are harder and more expensive to find.
So it's your choice, do you want the easyier path that is seemingly limited only by your money? Go A1200. Do you want the harder path that needs more money and patience? Go A4000.
Best of luck
