Which line for japan top tier air should i research first?

F15 line, F2 line, or gripen line? Grinded with F2a adtw.

depends on what you like

do you prefer HMD or aesa? if HMD f15, if aesa f2a

there are other differences ofc on how the planes fly and flight models

but if u like how the f2a flies and you feel it fits your style, go for f2a line. if you prefer more raw power but less maneuverability, then f15