sorry i probably didnt describe that really well, but what happened was absorbing lucas' up b once gave my bucket 3 charges.
If G&W absorbs the ball of Lucas's UpB, he will only get 1 charge for the bucket. However, it's possible to absorb the tail of the ball and fill a bucket without absorbing the ball at all. You can get a full bucket and still have Lucas's UpB traveling around. The bucket filled with just the tail isn't nearly as strong as if it was filled with 3 balls.
Try this. Get a Lucas and a G&W to stand next to each other, about a G&W length apart. Have the Lucas use UpB and move it towards the G&W with is bucket already out. What should happen is that G&W gets two charges, one from the ball and one from the tail.
Whats better when smashed(either direction) to bucket or to dair?
I don't understand your question exactly. Are you asking "What attack should I used after being sent flying away from an attack?" then the answer is ALWAYS Nair -> Bucket. There are very rare cases when the Dair, and its fast downward pull, will save you better than the bucket. But these cases so rare it's not even worth learning. Plus the reaction time required to realize such a case, it just won't happen.
If you're still curious, it has to do with stages that have smaller ceilings. Stages with larger ceilings should always be momentum cancelled by the bucket. Always!