General ACCAWhich is the best combination to take? F6 and F9 or F8 and F9

The ACCA recommend that the papers are taken in number order, and this is sensible advice. If you have already taken (or are exempt from) F7, then the better option is F6 and F9. This is because F9 does require a limited knowledge of tax (which is F6). You can learn the relevant rules on their own, but it is that bit easier if you have already studied F6. Alternatively, why not take F6 and F8? That way you have one 'numbers' paper and one 'writing' paper, and also you will be more prepared for F9 at the following exam sitting.