I prefer the hard type for better translation and more abilities. A problem is that hard type can be extremely hard unless you level up a lot (I used to run a lot from battles in FF4, and the game became hard), and it's even harder if you set battle speed to the maximum. I could beat (SPOILER)Zeromus with around level 58-60 party on normal battle speed, but on the max battle speed he's still really hard until level 64 or so.

There's one better feature about easy type, though, and that's in the Japanese easy type. In FF4j Easy Type, (SPOILER)Zeromus looks like a huge grim reaper. In FF4, he's a weird bug. IMHO, the reaper form looks more impressive, because that symbolizes hatred more than some bug.