I have all three of the first ones in english... 1 is absolutely solidly hard lol, especially if you dont level up properly throughout the game. It's good if you want a classic challenge. Personally, I'm a story lover rather than gameplay lover, so i think 6, 7 and 8 are the golden age, 7 being the peak, and ive played 'em all. I think this because:
7 has the perfect balance between good/bad graphics, good/bad dialogue lol, and AMAZING music played on crappy MIDI sounds heh, so that you can enjoy it as a game but you still have to use your imagination a lot, like an interactive book. It also has an awesome foreground/background story in general. Its incredibly easy, which is kind of annoying, but as i say, i love the story more that the gameplay. And I reiterate, the music is AMAZING. Nobuo Uematsu is an undisputed genius. Also, this game was, and few can deny it, somewhat of a revolution. It took everything further. Play it, and you're playing part of video game history. And on a lighter note the sub games rock! lol snowboarding, submarine battles, chocobo racing, motorbike slashathons and a few more random ones all await you.
6 is the most epic, not in graphics and sound obv, but in story. I won't spoil it for you, but take my word for it 😉. Again, the music, FANSTASTIC, though the sounds are worse. The story line splits, and you get to choose which one you play out first (awesome idea!) in a very non linear way. Definitely more of a good game challenge wise than 7, but without quite such classic characters.
8 is like the relationship between 6 and 7 reversed; the graphics are far better, the music sounds much better in terms of technology/acoustic affect, but It is the easiest of the series without doubt, and the characters are a bit cliche (especially squall) and the main villian is thrown in so badly towards the end that it kind of sucks. The whole Squall Rinoa thing (as you'll discover if you play the game) is also quite cheesy. Not that i dont love the story of course, i do, hence why i love the game, but compared to 6 and 7 i feel its weak. Be warned, the card game may obsess you. Oh and... The music RULES!!! AGAIN!!!!
anyway, that's my two sense. *Cannot wait for Advent children!!!!!!!!*