There's no one right answer to that. IMO, low reps(4-6) high weight makes me feel better cause i can tell i'm getting stronger. but, you can't do the same workout forever, you have to change up from high intensity to high volume every now and then and find what works best for you. Training to failure is always the best way to go, you really shouldn't do it for more than a couple weeks, but it can help you get past a sticking point, as well as partial reps and negatives. but no one type of workout works forever, and different people repspond better to different things.