Another Beatrix fan yay! And yes, that track is one of the best of the OST. <3 She's also the coolest character in the game too!Beatrix. But I love Vivi and Garnet too, because I think they show the most development throughout the game.
...Also, Beatrix gets points because "Rose Of May" is my favorite track in any FF game ever.
For me it would be Vivi. He's shy, cute, modest, smart and I think no one could actually hate him. Funny, clumsy Vivi and
all his inevitable stumblings. I felt really proud when he stood up to the Black Waltz attacking the cargo ship, like: "You think you can threaten me and my friends? You messed with the wrong black mage!". Even when he had discovered that his life would end soon, he did not go all whiny and pessimistic. He knew what was going to happen and he just continued his journey with his friends to make a difference and not to give up easily.
My favourite Character in the game is Zidane as well, he's selfless, caring, and a bit of a joker as well, he's good for humour and stuff, but also his character is very well developed, like his backstory, and how he deals with it when he finds out the truth.