Bit column vs relationships?
The bit-like field will make it harder to find all users or articles with a certain property. For users/permissions, that's not much of a problem (unless you want a list of e.g. all administrators). For articles, I can imagine that you want to filter on certain attributes (e.g. only non-18+ articles). You also have the option to store those fields (option 3) as single bit columns; then, no extra table is needed.

Another consideration: what happens when you want to add an additional permission/attribute which is by default set to '1'/'true'? For the bitmask field (option 1), this can be done by adding the right power of 2 to all values in column permissions; for option 2, you need a mass INSERT in user_permissions_map; adding an extra bit column with ADD COLUMN and DEFAULT true (option 3) is clear and easy.