I think new blood on Friday or extended
Silver is supposed to be the second least efficient of all of the packs, excluding Basic (Ultimate is in between the two). I've seen that the most effective (without relying on new releases/timing, so NB is out) is Extended, using the Frozn, Vortex, Fang Pi Clang, Sakrohm, Ulu Watu, and Piranas clans.
You can check this site: http://urdb.kirlad.net/packs.php
It's not perfect, and probability could drastically change the results, but you get an idea of the average clintz you get per pack.