FFTA. FFT was and is a great game, however, it suffered from many things, not limited to a terrible localization, an unbalanced battle system, and very inconvenient battle mechanics. FFTA improved upon all of this, with a much more balanced system, a very coherent translation, and battle mechanics that don't make you want to rip your hair out with frustration (with the exception of certain laws that involve not harming animals...). And FFTA is portable!

I will say that FFT had the better soundtrack though.

Of course, I'll probably like FFT a whole lot more once I see what they've done with the PSP port (whenever it'll be released, anyway).