Target selectors cannot accept multiple arguments of the same type.
To get around this, you should first create a dummy scoreboard objective like this:
/scoreboard objectives add Kill dummy
Then, in this order, run the following commands:
/scoreboard players set @e Kill 1
/scoreboard players set @e[type=ArmorStand] Kill 0
/scoreboard players set @a Kill 0
Now every entity that you want to kill should have a Kill score of 1, and Players/ArmorStands a kill score of 0.
All you have to do next is kill all entities with a kill score of at least 1: