Are high reps or low reps better for building muscle?
All strength training whether 1 rep or 30 reps will develop strength.
Training to *failure* is an inefficient way of developing strength and a very efficient way of building muscle size.
Training low reps with progressive overload is a very efficient way to develop strength and an inefficient way of developing size.
Why? It stresses your central nervous system to fail. But training to failure causes micro tears in the muscle which grow back bigger (hypertrophy).
You get stronger by (duh) lifting a weight you previously could not.
Go do 1000 pushups. Then try and bench press your highest ever weight. Impossible, right?
It is inefficient to get stronger by training to failure.