The most powerful of the brigades, militarily anyway, is arguably Jabhat al-Nusra, which I don't think is receiving any particular state's backing. Saudi influence is arguably more through the tribal confederacies and indirect arms shipments than anything else. You know, all of a sudden a bunch of Steyr rifles turn up after a guard group in Saudi decommissions them in favour of a worse rifle.
People think that the Saudi state is automatically in favour of Islamist factions, forgetting that an increase in Wahabbism doesn't necessarily benefit a regime already constantly walking a tightrope with the Majlis.
They are one actor amongst many, their influence being different to states like Turkey and the United States. I mean even France, since Hollande, is taking an active role in trying to turn the fighting their way.
The State of Saudi Arabia have no desire to see JAN or ISIS be the dominant resistance groups in Syria. Why anyone would think that amazes me. Saudi would love to see a group like Ahrar ash-Sham turn against ISIS and JAN. I have no doubt they have probably been asked by KSA to do just that and they have declined.
There are players who are looking to start a Sahwa like what happened in Iraq in 06-07.
More here for those that speak Arabic