There are so many variables that make up my favourite fantasy book. Good characters and plots for one. I like some magic, but not lots of it. I don't mind if it's set in our world or not, but I love different worlds. Mythical creatures are amazing, but it won't make or break a book. As for romance, not really. I like subtle hints of it, but not massive amounts.
I like it when the characters go on a quest or adventure. I like wars (if in a mythical world), and I like when a character loses someone they love. It adds depth. Justification is always good.