Recently I bought the 10+1 multi pack (when gems were on sale, 1300 for $7 or something) and I got pretty awful cards. One legendary, 0 new heroes and like 4 SR. I have gotten better drop rates for SR and Legendary just by opening packs one at a time.
I just assumed opening packs one at a time is better since it increases the randomness of the drops by giving a fresh set of drops each time.
