I've played both, and while the original will always hold a special place in my heart (Surrender or die in obscurity!), I like the new translation much, much better. I actually know what's going on this time around, and the colorful new dialogue gives the characters more personality.

As far as I know, Sony did the original FFT's translation, not Square - it's the same for FF7. So they didn't just go through the original and decorate it, it's an entirely new translation from scratch, done by the same people who translated FF12.