Personally, i like simple and clean because it was introduced in the first game. I like the first game because it introduced me to kingdom hearts and i like it ever since.
All for of them are pretty hard. first ,you should lock on to anyone but yuffie or cloud. Take tifa for example, first u gotta beat her up and when all her friends attack you, use Heal. now, u can either ur ethers or you can endlessly glide around the edges of the arena (it will be very anoying but thats how i beat them).When you glide, be sure to avoid them. When you MP bar is full, keep attacking tifa until she dies you may even use effective magic like thunder. to this with everyone.