FF8- never finished it but supposedly good.
FF9 was just fantastic, i played it twice on ps1 then again on pc (emulator), then on psp 2 times and now have it on ps3 too.
FF10 was a landmark title for ps2 and was great but ruined by the dreadful FFx-2.
FF12 was a masterpiece, it played like a proper RPG with real time battles and required strategy in fights. Stretched ps2 to its limits. I played the game on my PC with PCSX2 emulator and with high resolution and anisotropic filtering it looked great. This is a long game with a lot to do.
FF13 looked great but personally felt a little short changed as the above poster said that the real game starts 20-25 hours into it. A lot to do after you finish storyline but felt linear throughout, couple this with some of the most annoying voice overs of characters and an awkward story, it was not the best ff. Visuals however are great but the game did not warranted a repeat replay on my part.
FF13-2 is coming out which i have no idea why. Did not need to carry in my opinion.
FF versus 13 is something im eagerly awaiting for. Looks great.
Now back to OP question

. I would recommend that you play 9 as it was my favorite and want people to agree with me on this

.
then 10 and 12 and then 13, skip X-2 which was rubbish.