Depends what you enjoy most. My focus is on piecing and the strip dies are invaluable. Not only for strips, but squares diamonds and rectangles.
In my quest to rush into getting various sized shapes, I bought dies that cut a single square, rectangle, etc. total waste of money. They waste fabric and time.
If you like to strip your fabric stash . . .the 1.5", 2.5" and 3.5" are perfect. Additionally, I have many patterns that call for 3.5" squares, so the 3.5" strip is used often.
I made this top a couple of weeks ago . . .i started with a jelly roll and white yardage . . .but all the jellyroll strips were subcut and all the white cut and subcut using various strip dies. Whole thing took an hour to cut out and because the pieces were more precise than my rotary cutting, it went together quick.