Vagrant Story: because it is a complete game IMO, with regard to the important game elements like graphics, sound, story, etc. But the thing that defines this game and myself is the excellent gameplay, which is most important. I like good gameplay.
So far as SRPGs are concerned, I have to say Final Fantasy Tactics defines me as well. The gameplay in this game shined through, but it also highlights my love for sprites, those old school, 2D, hand drawn graphics – which is why games I also love games like Valkyrie Profile and Disgaea.
By the way, I played Front Mission on the PS1, and while I liked it, I found it a bit too long and too repetitious.
I actually recently bought Vagrant Story recently, I'm looking forward to playing it.
Front Mission is repetative, and I think customization is excessive, it does get tiring, but this was a fun game to beat, and the story really picks up near the end.