If I already had a copy of Panther lying around, I would, but if I'm going to have to spend money for it, I'd rather just get Tiger as a lot of things still aren't supported in Panther, like Flash 10 for instance, which is pretty much vital. I have enough extra memory sticks around here that upgrading RAM to offset some of Tiger's heaviness on G3 machines isn't really a problem.
I suppose I could also get either a plug in ethernet card or an Airport card for the G4 as a solution. I also have access to an eMac that would be an upgrade for a good price if I really want it, so I could go that route which might be better.