A is probably the best one in most scenarios as it eliminates the risk of the enemy unit taking advantage of the swap
C is probably the weakest because it literally screws over your own side of the field
I'd say B>C because compel isn't all that useful if you've already swapped it into your lines and also leads to more possibilities of the opponent taking advantage of the swap while with poison at least in some scenarios they'll just die on their own or your opponent will waste time trying to get some compensation for the dying piece