What is the best epoxy for broken screen

Once the glass has cracks, it has weaknesses. There's not really any cure for this. Any sort of adhesive you use is really just going to keep the pieces from moving much or falling out. I have seen people apply clear packing tape with the intention of continuing to use the device since it still worked fine, and if the cracks got worse or further physical damage happened that rendered the screen non-functioning (in this case you might lose touch response), they'd go ahead and replace the glass. Really, any choice outside of full repair of the damaged part is just a band-aid.