FF6 isn't totally non-linear by a longshot. And even though it's non-linear in the second half, it's not too difficult to figure out what to do if you just visit every place there is on the map. Also, I think FF1 has more replay value because you can choose a different party every time. To me, FF4 gets boring after you've beat it a few times.

"I am King James! Long Live the King!" - James FP