Well! it depends on how much you have to donate...
A +9 weapon will probably make u look "cool and scary" but usually it takes u about $20~25 to get up to +9 (2 packs of each red and blue if u're lucky.. 4 packs if u're rather unlucky.. like me
)
if you dont have a lot to spend.. say $5... then i'd say get the costumes with stats (extra defence/crit rates) coz with $5 you should be able to get 2 sets, each set lasting you a month