A:
Either the 6-6 medium or the 7-0 medium would work fine for senkos and flukes. The 7-0 would be my choice but I know some guys that like a little bit shorter rod for finesse style presentations.
If you look at some of the other manufacturers rods, especially the ones that are technique specific, most of the senco style rods are 6-8 to 7-0 in length in medium action with fast or xtra-fast tips. One key is to be in that 3/16 to 3/4 oz lure weight range, which these rods are.
The 7-0 would make a great Senko rod. Good luck this season!