Hi Lor
it depends what you are looking for. Do you want the sail for freestyle, and on what board? or do you want it for your biggest sail, and for some wavesailing too?
The Expression will be the better early planer, matched up with a 100l freestyle board you will go in almost anything.
For a more freestyle-wave, bump n jump, light wind wave board where you will do more wavesailing, go for the alpha