The best throw is whichever you master, as any throw can be adapted. But generally speaking the main problem with MMA is that it is harder to force engagement, along with strikes. So your window of opportunity is much less for throwing.
The way to solve this is to take more lock-up type grips and positions, which then favors lever type throws more (which do not rely on your opponent's movement as much).
However if you are a phenomenal thrower who can seize opportunities on the fly, then any throw works. It takes great skill to improvise grips and throw on first contact. I would say not even the big Judo names in MMA have really demonstrated this (not that they had to for the most part).