2. Assad is overthrown by the Muslim Brotherhood which sets up a Sunni Islamist dominated government. This is worse. Such a regime is likely to believe--mistakenly--that it can attack U.S. interests and Israel with impunity. The positive side is that this would constitute a major defeat for Iran.
3. Assad is overthrown by forces that lead to a regime of moderates, led by Sunni liberals, allied with Druze and Kurdish nationalists and with Christians. That would be better. Remember that only 60 percent of Syrians are Sunni Muslim Arabs and the Brotherhood has always been far weaker in Syria than in Egypt.