There are several countries that are more likely to successfully crack down on their movements because they can use external regional military forces to do so.
We are witnessing this in Bahrain where a very peaceful movement in a highly developed country is being crushed with the help of Saudi and Kuwait armed forces. Currently there are mass arrests and a state of emergency.
I'm guessing that Bahrain, Kuwait, Qatar, and possibly Oman and UAE are countries where foreign regional military intervention is most likely to succeed. These countries have a small population and strong regional ties (The Gulf Coordination Council).
Jordan also has a small population (6.5 million), but I think they'd *strongly* oppose intervention from Syria, and would also not want Saudi Arabia to get involved.
It is easier to crack down with an external military force who will not sympathize with the people. For instance China brought in army units from far away to crack down on the Tiananmen protest movement. Similarly Russian, not local, troops cracked down on uprisings in Hungary in 1956, and Czechoslovakia in 1968.
If you crack down with your own military, the power structure can fracture and leaders will defect to the opposition. This is happening in Yemen and Libya.
Bahrain is the least populous country in the region. It remains to be seen whether external military intervention will happen in other countries. Kuwait and Qatar do not show signs of a protest movement. Oman has one, but it might be in decline.