the original releases for the SNES of 4,5,6 are the japanese versions of 1,2,3
I have played every single Final Fantasy except for Crystal Chronicles and FFXII Wings of the Pegasus.
2/5 was really good for its idea that you could switch "jobs" (classes) for any character at any time except in combat
7 is by far my favorite because all the games have they fun factor but 7 took it to a whole new level, it is the only game that ever brought a tear to my eye (still does every time i hear Aerith's theme), and i prefer the materia system to any other so far.
I wasn't to fond VIII because i didn't like the fact that you had to "steal" magic and then not use it so you can improve your weapons/armor. also the whole limit break being completely random was kind of a put off.
9 was really good, i miss my copy of that
10 was ok except for what the enemy was named
10-2 was ok
11 is online only and really boring, you have to be a minimum level of 6 which takes awhile to get to in order even beat the first mission and then level 10 for the next one which corresponds to hours upon hours of eventless grinding.
12 - had a revolutionary system in that you could custom coat each character towards a unique job. plus as a benefit it was a continuation of FF Tactics Advanced and a prequel to FF Tactics (for PS1) which takes place long after either game when all the races except for human and chocobo are extinct