I use the PrintFile white plastic page hangers and dedicated four-drawer metal office filing cabinets. Not the most space efficient. But given sufficient space (an empty nest bedroom converted to a photo workroom for mounting, matting, and filing) storage is easily expanded by simply purchasing additional units.
The pages stay clean. They are very accessible (no digging required). Filing systems can be easily modified as needed. There is no weight compressing the negatives or slides. And it's all very clean and orderly.