“What is the best antibiotic for a tooth infection?”

That really depends on the infection as well as the patient . . . Any infection should be seen by a dental professional.

The only way to accurately answer your question is to get a sample of the infection and test it.another concern is to know whether you have taken antibiotics in the past, and how often...if often, then you will probably have bacteria that are resistant to the normal antibiotics. The best thing to do is to get rid of the cause of the infection. Taking antibiotics without taking care of the cause is like having an infection from a deep splinter, and taking antibiotics for it without taking care of the splinter. Get rid of the cause, then the infection goes away.
If the cause is a deep cavity that has not been repaired, and the tooth starts to hurt, due to the cavity getting into the nerve of the tooth, then you can have the infection cleaned out of the tooth by an Endodontist, and the pain will go away. Take antibiotic for the infection instead without either extracting the tooth or having an Endodontist fix it, means that the infection & pain will just come back. Fix the cause, not just the symptoms! If you take antibiotics without fixing the cause and then do it again when you've stopped the antibiotics and the infection comes back, it's a waste of time and builds up resistant bacteria in your body so that if you ever really needed some antibiotics for a disease, they wouldn't help.