[Iarwain Ben-adar]

I actually think that Sauron had a smarter plan to take over Middle-earth than Morgoth. Morgoth did not have a very good plan. From what I have read, his plan was to use his huge numbers and force to overtake and rule Arda/ destroy what the Valar made. He used fear and made people lose hope as his primary weapon. Sauron, on the other hand, had a much smarter plan for his takeover of Middle-earth; He gained the trust of his enemy, then Tricked them into making rings of power, and then secretly made a ring of his own so that he could enslave all of the others lords of the races that had received the rings. it was quite an ingenious plan, really. He only failed because of three things;
1)Aule made the dwarves tough so that they could endure evil and resist corruption, thus the lord of the dwarves could not be corrupted through the rings.
2) The elves took off their rings when they felt his presence through th one ring, or something to that effect. He could not rule them because the three rings were hidden.
3) When all hope seemed to be lost, Isildur cut off sauron finger with the ring on it, ad then Sauron lost the ring. If he ad still had the ring, or had never lost it, he would have been the ruler of middle-earth by the Third Age.
Morgoth failed because he had utterly lost most of his power because he put much of himself into his creations, and all of his evil deeds. You have to consider how much he put out of himself to become weak from beig te strongest and most powerful being in all of Arda, or the most powerful Vala. That is why he failed. Lord knows that he had more forces than Sauron, including the supervly powerful Balrogs and Dragons, plus trolls and other creatures. He had more army power than Sauron, but Sauron had the more ingenious plan. The ingenious plan is always better.