Anybody particular you have in mind?
To help out, I'll sum up my history with the series. I'm a bit partial to the old FFs myself - with VI being my favorite. IX and XII are the only post 6's ones where I really like the storytelling and characters. I absolutely hate X and XIII for gameplay reasons, but I have beaten X despite this fact. I didn't dislike X when it came out, but my opinions have changed as I've grown older. Oddly, my first FF was VIII which, though I find it to be one of the worst systems in the series, was obviously liked well enough to get me on board with the series.
As far as familiarity goes:
I - 3/4 of the way through, but N/A here really anyway.
II - Only played a little
III - Only played a little.
IV - Beaten
V - Beaten
VI - Beaten
VII - Beaten
VIII - Beaten
IX - Beaten
X - Beaten.
XI - Played for 2 weeks then quit in disgust with the mechanics. N/A here anyway.
XII - Played for a decent bit before my PS2 died. Would love to pick it up again, but never got a new one.
XIII - Played for a couple of hours before quitting in disgust with the gameplay.
The characters I DISlike from the series fall into 2 basic categories. You have ones like Vaan from XII and Tidus from X who are children that aren't particularly heroic. They seem to be protagonists only because young boy protagonists are the norm in anime/JRPGs. The others are ones like Cloud or Squall that, while they seemed new and cool when the games came out, really boil down to just being emotionally stunted, hollow, emo dudes. I get that "Leave me alone, I'm too mysterious and dark to care" is the fantasy guy for some ladies, but I don't find it makes for a compelling character.
On the other hand, I like a great many more of them. Balthier from XII is basically an example of my go-to RP archetype. Anybody who's well written, has a good arc, and is defined as an individual and interesting person I wholly dig.