I would go for the SNES or Rom version as my first choice. Just to see the classic charm. Then I suggest palying the GBA version cause the new translation does wonders for the characters and story. I always felt like I only loved FFVI more than the others because of the nostalgia but after playing through the GBA version I can honestly say VI holds up to todays standards of character and plot and in some cases I feel it's better than some of the later games that SE gave us.

It's not as linear as the other FF's either, it actually has more non-linear elements than VII and VIII. The PSX version isn't that bad either and to be honest the only times you'll really feel load times is during saves and going to the menu screen. I personally feel Chrono Trigger suffered more than VI did in the porting department.