Depends on if you have lots of weeds where you will be sailing.
If lots of weeds, use the True Ames SW Weed.
It's not really too big for a Futura 141 with a 7.5 m2 or larger rig.
If you sail somewhere with no weeds, then try the 50 cm Drake.
In weedless waters, the more vertical fin will give you a bit better
performance and a little different feel.
Hope this helps,