Would you use a screen protector on the iphone 6s?

With 3d touch and all that?
if yes, then would a tempered glass one work as well?

Nope

Basically a screen protector is used to keep the screen from getting scratched. As many people have fund over the years, there are many things out there that are harder than glass that can scratch it, just going in and out of a pocket, purse or backpack, in the form of plain old fashion grit.

Now while a tempered glass type protector is better scratch protection, and a tiny bit better shock protection, but any jolt, jar, drop onto a hard object/surface or any hard object dropped on the phone (front or back) can break the glass screen protector AND the glass screen under it.

So you have to decide from yourself, is it worth the cost difference in a plastic film screen protector to get one, if the screen under them may break on drop #5, and once broken, the screen will have to be replaced anyway? For me the answer is no. I can replace several plastic film protectors in a year or two, and still not pay what most people are paying for the glass ones. But everyone I know (every single one of them), that have opted for glass screen protectors, not only broken the protector, but the screen under them as well, more than once.