whats better for gains, training to failure or not training to failure?
When doing a set for any exercise with a weight that is less than your one rep max all the muscle fibers do not act at once. With each succesive rep more fibers become fatigued which forces the muscle to recruit more fibers.
Training to failure with a wide range of reps and loads is the only way to recruit as many muscle fibers as possible. The more muscle fibers recruited the more productive your training.