Iran.
There are many problems for the current regime.
It's a multi-ethnic country with Persians only at ~51% majority. Islamic fanaticism was eroded by modernism. Most people is fed up with the Muslim regime. Many people with differing ideas, depending on social background and education too. They seem to be ripe for divide et impera.
However whoever comes to power will face the same problem. The shah (his son actually) is hated the same like the Islamic Revolution. And anyone else is just too unknown and smalltimer to gain majority support.
I think if the current regime is toppled and the new one is supported by USA and Israel, there is a great chance that this puppet regime will do massacres and oppression.
Otherwise the country might fall into chaos, or rather anarchy, some parts may even secede. More instability in the region.