in vs out for odor control

hey. i just wanted to know your opinions on putting a carbon filter on the intake side of a dayton squirrel fan (before sucked in) or on the exhaust side (after blows out)? does one work better than the other? i'd prefer it on the inside so it'll be more contained but if i have to put it on the outside thats what i have to do. i'm growing 3-4 plants in a 3x3x6 box so space shouldn't be a problems. thanks ya'll