No. 6 Final Fantasy VII (PS, PC, PSN on PS3 & PSP)
The first 3D final fantasy, my first RPG and my favourite in the series. I had avoided most RPGs prior to this as I wasn't much into fantasy (oh how times change!) and they all seemed to revolve around fantasy settings. FF7 completely changed all that. A fresh new cyber punk world, an eclectic mix of characters, a combo of bizzare science & magic and ridiculously gigantic swords! The first 3-4 hours spent in Midgar & Kalm drew me into the story (and is probably the best intro to a JRPG I can think of) and then the apparent freedom of the world map completely astounded me.
Looking back this had nearly everything I want in a JRPG. The story was intense and emotional but it also had a great degree of freedom and player choice in the game world. I'll admit, the materia system isn't the best system in a JRPG as it didn't give a huge amount of customisation, and many characters seemed to be very similar no matter what materia you added. However, the plot, the world, the towns and hidden extras all made up for it.
I also think the optional quests were some of the best in a Final Fantasy game: Chocobo breeding and racing, two optional characters with backstory, the Weapon bosses, the mini-games (Submarine, snowboarding, motorbike), the range of vehicles, the hidden locations and the little tit-bits of backstory. All added to an utterly amazing game.