1 is novel but boring
2 sucks
3 sucks but its kind of like ff5
4 is like the template for the series and introduced a lot of mechanics to the series
5 is fucking MISERABLE to play but the job system is new and the story/setting is kind of interesting
6 has the best setting and a decent story and good gameplay variety but the pacing is horrible and you spend so much time in menus. at least 20% of the game is menuing.

Play 6 then 4 then dont play any of the others