The Helix On Nemesis, without a doubt. The force generated on the way out of it, especially in the back row is pretty damn crazy, plus your feet are about 2 feet away from a fence and a wall all the way round it.
The final helix on Nemesis Inferno, just before the brakes is also good, really intense g's.
The helix on Nitro was really good because it had good force, although not as intense of a force as on the two Nemesis coasters, but it lasted for ages and ages and you could feel your neck crushing