what game should i get

Both.

Depends on you, what you prefer. I'd pick the one with bigger discount.

Chivalry. Wait a goty/complete version of Sleeping Dogs.

i haven't played chivalry but Mount & blade is one of the best medieval warfare game there is

I'd say Sleeping Dogs, because Chivalry is not that good.

Chivalry is fun, but I feel Sleeping Dogs will get you more gameplay value, especially if you're not playing Chivalry with friends