Hidden Arsenal was a great idea on Konami's part, but some of the pack series in Hidden Arsenal just aren't as good as some of the others.
My list, favorite to least:
Hidden Arsenal 4: Trishula's Triumph: It has Trishula, one of the GREATEST cards of ALL FRIGGIN' TIME.
Hidden Arsenal 1: It has Brionac, another great monster, plus, it started it all.
Hidden Arsenal 3: Considering the only cards I ever wanted from it were Dragunity Knight - Gae Bulg and Dragunity Phalanx, it just left a little to be desired.
Hidden Arsenal 2: I just could never find anything I liked from this set besides a few support cards for the HA1 archetypes.
What do you all think? Post your own list, with reasons