Scrolls is by far my favorite digital TCG, but I do play Hearthstone occasionally.
Hearthstone is kind of a shitty game. The mechanics weren't immediately engaging (it really does play like babby's first TCG with training wheels), and updates are way too far apart. The game has literally not changed in about half a year, and considering it never had much depth to begin with, it gets real boring playing against the same deck over and over again for months.
Also the new "expansion" has really made me dislike the game even more... they're already introducing DLC into a free to play game. You have to individually buy each "adventure" where you get the new cards (which looks like they're introducing power creep already, btw).