Dr. Boom
Sylvanas
Ragnaros
Alex
in that order. Class cards like Grom and Antonidas are as good. Everything else is unnecessary if you ask me. (for ranked play)
Malygos become more playable in Malylock but it seems the popularity is dropping. Handlocks don't need either of their class cards but they are cool and usable.
Rogue legs are both obsolete. Shaman, lol, Paladin's Tirion is ok, but it's not needed. Priest's are meh. Hunter? no one ever plays those. Druid? I don't play but nothing you can't replace with other cards, they're no game changer like above cards.
If you got any of Ysera, Deathwing, Thalnos, Malygos or above mentioned class cards except Flame Leviathan and Iron Jug, don't dust them. Worth keeping but not crafting.