You said your few buckets never collect much, but maybe that's because of where you put them, @richard_king. If they are under a tiny part of the roof or a spot that doesn't drip much, they won't fill up. A bigger barrel right where the water pours off the gutter can get a good amount really fast. Sometimes it's not about having more buckets, it's about putting the one you have in the right place.
Check if your roof material even lets water run off right, like Jennifer said about placement but also what it's made of. Some just soak it up or splash it everywhere.