The G4 are too slow for a lot nowadays. I would get the Intel model, not just for the great speed bump but as you have seen besides software limitations, most is Intel only anymore, internet has it's hiccups now on PPC. G5 can go to Leopard. The late 2006 models were the Core 2 Duo and can run Lion, the first two 2006 Core Duo models are stuck on Snow Leopard.

Make sure the LCD display doesn't have any lines when lit up, both the G5 and early Intel models had problems with that. Apple replaced them under an as needed recall.