Prophet Skeram
Chieftain
I think it has more to do with what type of map you choose, the layout of the map, and what the AI does. Though the autoplant quest does play a factor.
The Ultrasonic Fence quest also is a factor. I've had several games where it took over 5-7 turns to pop and I was quite worried it might be bugged. Getting trade routes started without it is usually truely awful, and that's with me wiping out all aliens on sight whenever possible.