It probably depends in if you're building tank Akali or AP assassin Akali. My bet is that tank/bruiser Akali uses all 9 hybrid pen marks, while assassin Akali prefers either 9 magic pen marks or 5 magic pen/4 hybrid pen marks.
Protip: penetration quintessences aren't any good, don't buy them.
Protip: penetration quintessences aren't any good, don't buy them.