Well, both are viable options, and i would just let it up to you to decide you favourite.
Shuppet (M) @ (No item)
Shadow Ball (Shifts attention when needed) 3 hearts
Hidden Power (If you feel like spamming) 3 hearts
Psychic (Scare some little pokes!) 1 heart, 3 black hearts
Destiny Bond (Finish him!) 8 hearts, miss a turn of appealing.
Koffing (M) @ (No item)
Toxic (Worsening condition :D) 3 hearts
Pain Split (BOO!) 1 heart, 4 black hearts
Hidden Power (Once again spam or just a general great move) 3 hearts
Destiny Bond (WTF BOOM) 8 hearts, miss a turn of appealing.
Its your opinion, but I think that Shuppet has a slight edge