The first set I bought was the Go Mix and Match 12" because I could make 6" or 12" and even 18" blocks. I used them a lot. I Think you would find similar flexibility with the Ready Set Go with the 8" block and all of the other go and it is a great price right now.
There are a lot of videos on utube on how to mark and use the dies. Marking the dies helps when positioning fabric and if you stiffen your fabric (I starch mine board stiff) you don't have to be as careful about grain lines (especially helpful when using scraps) and if the pieces are stiff when you sew there is less stretching.