EASIEST
FF8 (really easy to make your guys invincible)
FF7 (easy as well)
FF6 (this one's also easy)
FFX (if you do all the side quests, it's pretty easy)
FF9 (pretty easy, but has a few hard parts)
FF3j (a lot harder than the ones I mentioned above, but not impossible if you level up enough)
FF2 (it can be hard at times, but you can beat it without cheating)
FF1 (it can be very hard with a bad team; some parts are still challenging even with a good team)
FF5 (pretty tough, but fun)
FF4 Hard Type (the hardest for me, some dungeons are really hard, especially the last one)
HARDEST

I find it weird how FFs ever since VI have been a lot easier than the Final Fantasy titles on NES and SNES.