I postponed starting this challenge for some time simply because the first question is hard to answer; all the three games I've played have been good and have something done better than others. I also haven't played all of them same amount of time, so from that point it's bit unfair to rate them yet. Especially since my current playthrough for the 3rd game is still unfinished, and been so long since my last playthrough that I can for example barely remember how fun the last hours were.
But not able to finish it for some time, I decided to simply choose based on the current feeling. And because of that my favourite would be FF2: DCB. Why? For once, because it is very enjoyable to play for most of time. I have finished it three times and still haven't grown bored, instead trying to complete the spirit list. The gameplay is much smoother than what I remember from the original game, and I think it took the best gameplay elements from FF4 and fixed them better. The fighting is smooth, I prefer over-the-shoulder view to the fixed angles, and the pretty graphics really bring the village even more alive. I also gotta love the more detailed character designs. And second, the ritual, the story and the setting have always been my favourites in the series so far. Even if the story is basically just about finding and losing Mayu all over again, the background and the village's history make up for that, making the whole place so interesting and exciting that you just want to explore every corner to gather all the information. It is not a perfect game, not at all, eg. with the lack of random battles and scares and the lame Haunted House mode, but it has gotten me to play it more than the others combined together. Something about the twins' tragic trip to the village and its even more haunting story keeps bringing me back~