The Disney ponchos are the best because of the thickness and durability (you can take them home and wash them in the delicate cycle). However, that makes the Disney ponchos a bit heavier to carry around with you. But, we still have our Disney yellow ponchos from way back when those were still offered and they are going strong.
We have also used the cheaper dollar store ponchos since we can cram those into a pocket for a day when rain "might happen" and usually doesn't. But, we keep those or take them home to be recycled.
For a true storm, Disney ponchos. For a light rain, the cheaper ones.