Hardest is a tie between XII and XIII. XIII started out easy and got hard towards the end and I was so unmotivated by my distaste for the game that I didn't want to bother. XII I did enjoy but it got difficult for me around the Phon Coast. Man that game was long. Tactics also gets pretty difficult.

It's hard to say easiest because some of them like IX and VIII I have played them so many times I know them like the back of my hand. I would actually say VII. I had never gotten past the beginning of disc 1 before last year and I tried since it is tied for my boyfriend's favorite FF game. It was actually really easy. Leveling was easy, the materia system was easy, boss fights, even the ones that I was initially scared of, were easy. I noticed a difference between VII and IX for example, in that IX you could finish the game at probably level 40 if you put little effort in to grinding, and it took me FOREVER to get to level 70, which is where I wanted to be. In VII I got up to level 60 without trying too much and it took very little time after that to get to 70.