Mine for sure is Keepsake key. By far.
Followed by bank boosters.
I think some packs/items are overpriced, but I believe this is how economics work - better it is, higher price it can hit.
I'd like to see more 'extra features/items' in SGS; such as: Item recolours, Eye-gazes like abilities, and more packs from our beloved in-game heroes!
Yes, please.