I'm totally hooked on gwent, I like all my decks I've built so far but gotta say my strongest and go to is my nilfgard using max 25 cards 22 from offense and 3 special cards with decoy always on.

Dude there is a merchant in the corner inside where you meet the rat king, and the loan shark in valen they both have monster decks that are stacked and really fun to play. Skelige has a few barkeeps that have stacked decks too.