Few questions:
1) Do Marks still generate Quanta each turn?
2) Are creature quanta generators excluded, for example Rustler, RoL, Damselfly, etc.?
3) Does the opponent suffer from this same quanta limitation?
I'm thinking poison will be a good choice, 3 damage for 1 quanta is hard to beat. Fire spectres, Lava golems or Forest spectres with their growth quanta being generated by mark (if Mark generates each turn) would give consistently growing damage against shields. Damselflies (despite generating quanta) are a 2/1 creature with no cost and upped Sundials can stall without a cost.