Mushroom plug from the inside. It's been a few years, but when I researched the topic that was the only repair acceptable to the major tire manufacturers -- with the caveat that any repair derates the tire speed rating.
(A mushroom plug is a combination rubber plug that goes through the hole and an integral patch on the inside of the tire. They really work well)
I have no doubt that this (patch-plug) is the most secure tire repair. Even if it leaks, it won't blow out like a sticky string might and if I had access to a tire machine, that is what I would use, despite the fact that it is far more time-consuming. (Many MC places won't patch a tire under any circumstances.) I used patch plugs a couple of times a few years ago when my friend (RIP) owned a complete commercial tire machine and balancer.
That said, I have never had a sticky string plug fail (yet). A drywall screw straight in is probably the best scenario for a string repair. Small hole, rough sides, unlikely to have caused damage to belts (although you should always look for evidence of tire deformation, no matter what sort of repair).
For anyone who hasn't done a sticky string repair, don't assume you will get it right the first time! Good idea to practice on an old tire to get a feeling for insertion, amount of glue and the "twist" upon removal of the tool to create a knot on the inside that won't easily blow out.