Honestly, antibiotics and their strengths depend on the ailment that you have, as they use many different types for different infections. Sulfa antibiotics are still the strongest for urinary infections, and the old stand by, Penicillin is still widely used. They have antibiotics that is taken only once so those are pretty powerful, like Vancomycin. The reality is taking antibiotic in any form may build resistance and make it less effective the next time.
antibiotics may be taken by prescription but it is widely used for example there is ofloxacin for urinary tract infection azithromycin for respiratory infection augmentin for general infection cefaclor & zinnat for digestive &urinary trat infection