Physalia hands down.
You run into a delay or fire shield or thorn shield what? 2 Games out of 100 in pvp? In champs league, I haven't seen ANY thorn or delay shields, and the only time I've seen a fire shield is against a fire stall which speed poison loses to anyway since it has fire storms and rage elixirs to deal with both chrysoras or physalias (not to mention SoGs).
In a game without a shield blocking you (most of them):
Accumulative Damage
Physalia's Damage, Chrysora's Damage
Turn 1: 2, 0
Turn 2: 5, 1
Turn 3: 9, 3
Turn 4: 14, 6
Turn 5: 20, 10
Turn 6: 27, 15
Turn 7: 35, 21
Turn 8: 44, 28
Turn 9: 54, 36
Turn 10: 65, 45
Turn 11: 77, 55
Turn 12: 90, 66
Turn 13: Dead, 78
Turn 14: Dead, 91
Turn 15: Dead, Dead
So a single physalia will kill two turns earlier than chrysoras. That effect is heightened when you add even more physalias/chrysoras. Its well worth the risk when you run into one of those three seldom-used shields.
So you see, physalia. Hands down.