Which option would be more effective in preventing moisture-related print failures?
Let's look at the options:
Using an airtight storage box with no holes for filament storage when not printing.
And I assume printing after getting it out of the box to put it back after printing. This is excellent for long time storage, it is much simpler/practical to use vacuum bags instead of a box.
I use this method on one of my printers, works fine if the filament isn't out of the box/bag for days. For shorter runs I've printed even Nylon like this, but note that it might depend on the filament brand. Another member commented that they did encounter moisture problems when exposing Nylon to the open air in hours. This also depends on the moisture in the air.
Placing the filament spool inside an airtight box during printing, equipped with roller wheels and a small hole for the filament to exit.
This is excellent for short time use when printing.
For one of my printers I use both (this is a large size printer, so long prints are possible), for another only the long time storage (smaller printer for relative small/short prints). Both methods of operation work fine.
It takes time for filament to absorb moisture, so generally, the first option should be sufficient. If not, you could dry your filament in a dryer used for drying food.