A General Argument from Evil:
God (def.): An entity that is omnipotent, omniscient, and morally perfect.
Omnipotent (def.): An entity G is omnipotent if and only if G can do anything that is logically possible.
Omniscient (def.): An entity G is omniscient if and only if G knows every true proposition.
Morally Perfect (def): An entity G is morally perfect if and only if for any two acts, events, or states of affairs A and B, if A is morally preferable to B then G prefers that A occur or obtain rather than B, and G acts accordingly.
NOTE: The notion of ‘morally preferable’ presume no particular ethical theory. The argument that follows is neutral as to correctness of any particular ethical theory, and as such is applicable regardless of which ethical theory is correct.
1) God exists.
2) There has occurred at least one event E such that E brought about unnecessary suffering; suffering not logically necessary for the bringing about of greater good.
3) Since God is omnipotent, God could have prevented E from occurring.
4) Since God is omniscient, God would have known that E was going to occur.
5) Since God is morally perfect God would have preferred that E not occur, and acted accordingly.
6) If (3), (4), and (5), then E could not have occurred.
7) Hence, E did not occur.
8) But, by (2), E did occur.
9) Hence, either one or more premises (1) through (5) are false.
10) Premises (2) through (5) are true.
11) Hence, premise (1) is false; God does not exist.
This is a valid reductio, so the theist must reject either theism itself, or at least one of the following premises: (2), (3), (4), or (5).
If you think the conclusion of this argument is false, then you are thereby rationally committed to the claim that at least one of the premises is false. So, explicitly state in your response which premise you think is false any why.