Sildenafil and tadalafil are the two most common treatments for erectile dysfunction. Both help most men who try them, and both are now available as cheaper generics. The real question is often not which one is "better", but which one fits your routine.
Sildenafil is typically taken about an hour before sex and lasts around four to five hours. A high-fat meal can slow it down. Generic tadalafil, on the other hand, can last for up to 36 hours, and food makes little difference. Plenty of men also take a low daily dose of tadalafil so they do not have to plan ahead.
To compare the two in more detail, see this plain-English guide covers doses, timing and safety.
Safety first: never take either medicine with nitrate tablets or sprays for chest pain or with "poppers". Let your doctor know about any alpha-blockers. The usual side effects are headache, flushing, a blocked nose and indigestion. Get urgent help for an erection lasting more than four hours or any sudden loss of sight or hearing.
Strength matters too. The licensed doses are 25, 50 or 100 mg for sildenafil and 2.5 to 20 mg for more info tadalafil. Bigger doses do not reliably work better, but they do make side effects more likely. Only take the dose your prescriber has set.
When you buy generic ED tablets online, check the strength on the pack and keep the leaflet. A valid prescription is required for every order of a prescription medicine. You can read more in this tadalafil and sildenafil guide.
This is general information, not medical advice. Always check with your doctor before starting a new medicine.