final fantasy tactics and jeanne d'arc are tied for me with disguea being third.

FF Tactics.

Well first and formost, I'd say get Jeane D' Arc, it's going to end up being the hardest one to find :x and at the moment, it's probably the cheapest :P Get it while it's still around!

Disgaea afterwords, it's a niche title, and there probably won't be too many of them released ^^

Tactics is great, and probably the most easily available :P But the slowdown issues are so annoying sometimes! They just drag the battle out :3 Still a great game, and one of my favorites :) The Different jobs were just so cool XD

Level-5's Jeanne D' Arc

Actually, FFT has just become the greatest hits lately, so it's currently cheapest.
Jeanne D'Arc will eventually follow the suit because it's published by SCEI.

Disgaea, the other two are decidedly inferior since they are not Disgaea.

I'm probably going to get Disgaea 3 for my PS3 and then FF Tactics for my PSP...when I stop procrastinating and actually get off my butt that is :P