I am currently doing F9, I would just like to know which of F6, F7 and F8 would be best to do at the same time. I have those 4 left at fundamental level so I want to be sure which would be easier when done during the same study period.
It is difficult for me to say because I don’t know your strengths/weaknesses or likes/dislikes.
F8 (written) provides a good contrast to F9 (lots of calculations). F6 and F7 both have a lot of detailed facts to learn: tax rules, IFRSs. Have a look at the syllabuses and a couple of past exams.
As this question started off about F9, better to post it on the F9 forum.