99.99% is carboy w/airlock. Rarely, once already clear, aged and gas free, I'll move to gallon jugs w/screw caps when I need a free carboy.
Right now the only thing I have in gallon jugs is a 3g batch of banana I did A Long Time Ago and I'm not sure what I'm going to eventually do with it beyond experimentation. I haven't even tasted it yet ...