If you want crossbody, I think you'll want the longer one. You can hang a measuring tape over your shoulder to see where the top of the bag would hit on you. I think the original Coach straps were 36 inches. I don't think the width matters since the clips are all the same size. The wider the strap, the more comfortable it usually is. Thinner straps might dig into your shoulder.
Thank you for replying so quickly. I am going to use a measuring tape but most likely I will stick with my original gut feeling of a 1/2" wide and 45" long strap.