Best Combination with F9

I really do not think it makes any different which one you choose because neither P1 or P2 have any real connection with F9.

The only thing that might be worth considering is the fact that P1 is almost all writing whereas P2 has calculations.
(F9 is half calculations and half writing). Whichever you choose this time, then it will mean that next time you will have either P1 and P3, or P2 and P3. P3 is almost all writing.

I always think it is best to have a written paper and a calculation paper (rather than two written papers at the same time). For that reason I would choose F9 and P1 this time (and then P2 and P3 next time).