chrono cross is great! =) i hear the music is pretty good.
each FF game has positives and negatives, in my mind. it's worth noting that FF4 - especially the updated versions available on modern handhelds - is an excellent game as well, and shouldn't be overlooked. but this is about the 3d games.
7's graphics are pretty poor nowadays compared to any of the other games, but the story is still solid enough and the gameplay isn't as dated as you'd think. the places in the world are well realized as well which is fun, and the music is iconic. i haven't played 8 since high school, but i remember the story being more disjointed. the gameplay was interesting enough and it was fun exploring for magic to draw, and there are some really timeless themes in that game as well. i also haven't played 9 in 10+ years but i remember the characters being fun and the art style being fairly unique among the more modern FF games. i didn't enjoy it as much because i preferred the more serious settings of 7 and 8 over the more extreme fantasy bent of 9.
among the PS2 games, X is one of my favorites, and if you can play the PS3 or PS4 remakes it's worth it. the story's pretty solid (only a few leaps of faith needed) and i liked the characters. the addition of voice acting is nice too although it's pretty stilted...if you don't mind listening in japanese and reading subtitles it's better. i really enjoy the battle system and progression system in X as well, and the crossover island/steampunk setting is pretty well done. i enjoyed X-2 more than most - it's definitely more cutesy/fanservice than it is a 'real' FF game, but the dresssphere/battle system is pretty decent (13-2 lite, kinda) and there's some replayability if you like it. XII is a great break from tradition in that the art and style of the game is similar to the older games, but it feels like an MMO in how you roam the world. it's too short, vaan clearly wasn't supposed to be the main character, and the story kinda goes to pieces in the second half, but i enjoyed the gambit system and the characters that aren't 12 years old.
if you get a chance to play the newer games, XIII and 13-2 are definitely not as bad as reviews say. XIII holds your hand for way too long (they don't really take the shackles off the battle system until almost 25hrs into the game), but 13-2's battle system, monster catching, and progression are all fun, and seeing the world in different forms depending on timelines is fun as well. i really enjoyed 13-2's battle system, enough that i would consider it to be one of my favorites in the series.
if i had to rank 7 through XII, i'd say that i found 7 and X to be in the top tier, 8 and XII in the upper middle tier, and 9 and X-2 in the lower middle tier. i definitely don't think any of them are bad, they all have very specific things that are really awesome about them. i just preferred the gameplay and characters of 7 and X the most.
edit: derp, you wanted to know where to start. if you've already seen 7 and 9, IMO X was my next favorite game, so i'd start there, or else maybe go for 8 and complete the PS1 trifecta before moving onto PS2. don't start on X-2 as there's a lot of assumed knowledge of X in the game and some spoilers.