I maybe in the minority, but I really like the Harbour Standard Longboard Fin when riding my 10' Rapier.  I have tried the HP fin and found it ok, but I thought my board and surfing was much better when using the Standard. 

I have a 10' Merlin now too.  Maybe I'll try that fin out in the Rapier for another comparison.

I know it asked about a Banana, but I didn't want to start a whole other fin thread.