Decisions, decisions....
Back in the 80s Israel lobied for the war between Sadaam and the Ayatolah to last as long as possible. That's pretty much my attitude about this whole affair: Pox on both their houses!
The great thing about a Moslem civil war is, everyone wins.
Okay, now brace yourself...
Definitely the Iranian proxy. The Muslim Brotherhood (through its military wing al Qaeda) carried out two attacks on the World Trade Center - in 1993 and 2001. In total, it has killed 10,000 Americans, via the World Trade Center attacks the terrorist attacks in between and the wars that followed. Besides 90% of the world's Muslims are Sunnis. Until a better balance of forces is achieved, it would be prudent to root for the weaker of the two powers.
Iran is a big talker, but it sued for peace after losing less than 1% of its population during the Iran-Iraq War. In WW2, the Germans, who never had this view that death in battle meant a straight shot to paradise, fought until their capital war captured in 1945. They lost 10% of their population. Bottom line is that talk is cheap, and the Iranians have indulging themselves accordingly.