I plan on applying to some of the top US grad school programs upon completion of my BSc. Just wondering if, in the case that I am not accepted into my top choices, it would be worth doing a Masters before reapplying? I realize having a masters will probably make me look more attractive to the top PhD programs, so I suppose my main concern is whether or not this would have any affect on the duration of my PhD? In other words, after completing a 1-2 year masters program, could I perhaps bypass the PhD coursework or at least shorten the length of the PhD degree by those 1-2 years?
Also, I would have the option of completing a masters by research or coursework. Which would be favourable in the eyes of the PhD admission committees?