What box on old set is best to buy?

[HeroOfLegendsSP]

I have most of every card of the DPPt and HS sets in my collection, so I don't really need to buy boxes from those. However, I seem to lack many cards from the Base, Neo, and E-series, and of certain sets from the EX series. Here are the sets I have the least amount of cards in:

Fossil
Gym Heroes
Gym Challenge
Neo Revelation
Neo Destiny
Expedition
Skyridge
EX Hidden Legends
EX Emerald
EX Legend Maker
EX Crystal Guardians

Which box should I buy cards from? I have a hard time deciding between Gym Challenge, Neo Destiny, and Legend Maker. Any other sets from what I lack other than Power Keepers, Delta Species, Team Rocket Returns, and Sandstorm.

 

[omahanime]

There is a thread for this. The "What Should I Buy?" Thread