choice scarf or band

i have a cloyster with
EVs in
defence 252
attack 248
speed 8
with the moves
icicle spear
razor shell
iron defence
shell smash
with the ability
skill link (max's out muti strike moves like icicle spear)

Don't use either. Your Cloyster is a set-up sweeper with a boosting move (Shell Smash). The choice items are going to lock Cloyster into one move, making Shell Smash useless. Cloyster isn't very good with the choice items to begin with. Use either White Herb or Life Orb. White Herb removes the stat negations from one use of Shell Smash, while Life Orb just gives an added boost of power. I recommend looking at Cloyster's Smogon analysis, because there are a lot of problems with your moveset.

Please use the Competitive Team Questions thread if you need further help.