Which one to focus on levelling up ?

Hi, so I play with all 4 planes occasionally. Don't really have a favourite. I have been levelling them all up slowly ... Cuz thats what you do in most video games right? Level up everything? But now I have seen some comments on this subreddit that it's better to level up one plane to lvl 8 then 16 as soon as possible. So which one should I foucs on ? Also what is the deal with trophies ? Should you have/not have them ?

Hi, so I play with all 4 planes occasionally. Don't really have a favourite. I have been levelling them all up slowly ... Cuz thats what you do in most video games right? Level up everything? But now I have seen some comments on this subreddit that it's better to level up one plane to lvl 8 then 16 as soon as possible. So which one should I foucs on ? Also what is the deal with trophies ? Should you have/not have them ?