Our choice of Rod & Staff math is strictly personal preference. We just prefer the structure and review of R&S, and we feel students are more successful in math if they stick to a topic until they have mastered it. R&S is structured so that students work in one area of math with lots of practice before moving on to another area. Then, there is built-in review in every lesson. R&S for younger students concentrates on basic math - addition, subtraction, multiplication, and division. Addition is practiced throughout a unit until it is mastered. Then, the students move on to subtraction, with a few addition problems for review each day. But the majority of their time is spent practicing the one process they are working to master.
R&S also begins with a thorough review each year before moving on to new material, and we find students need that review after a summer off.
This is not to say that Saxon doesn't accomplish the same end result, and I think you could be equally successful with either program. It is just a matter of which program you feel is best for the way your students learn. I think that Saxon works well for students who are innately good with math and enjoy the challenge of jumping around, but when I was teaching, I found that my math students who struggled with math concepts did better with the structure and repetition of R&S.