Newtons to push jacks is unreliable in many circumstances, but mainly because you cannot push jumpjet units while they are jumping. They just completely ignore all impulse applied to them and will land exactly where they are told to. That's why recon commanders can break free of a jugglenaut.
If the building is raised and the jacks have to jump to reach it, then newtons can push the jack away after it jumped. Odds are the jack will get a couple of hits in while jumping and then land on the ground, getting pushed.
If the building is not raised the jack can jump near the building and the newtons will only push the jack into the building, doing nothing. If the newtons are set to pull, then the jack will destroy the newton and then go to the building anyway. It's worse if the building is against the side of the map because the jack can jump just behind the building, slightly outside the border of the map and then no land units can reach it.
If the building is sunk, it's even worse. The jack will just jump into the pit ignoring the newtons completely, fall into the pit and destory the building.
Gnats work. Racketeers work. Enough towers that have a cylinder targeting system work (pickets and gauss) because they have infinite vertical range, so they can shoot at the jack while it's so high in the air nothing else could hit it.
That doesn't work very well, but you can also build charons and give them a pick up command on repeat over the singus. When a jack gets near, the charons will try to pick it up automatically. It can work, but it's a bit unreliable because the jack can attack the charon or just be ordered to move around the building. If the jack stays in motion, it is likely the charons will just never be able to grab it.
I find racketeers to work best. They'll just disarm the jacks while in flight and then you can dipose of them in whichever way you happen to have at the time. If you think that's costly, well, consider that you won't lose anything at all that way since the jacks won't be able to attack and also that odds are whatever you need to spend in racketeers, the newton ramp probably cost as much or more.
