I know, I know....this is a totally generic topic for my weekly advice post, but I think it's too important to ignore. There are so many people out there who decide to write a paranormal romance novel because it's "the thing." Same with dystopian, which has grown more and more popular over the past couple years. Now, if you've always wanted to write a dystopian story, good for you. Go ahead. Knock yourself out. But if you choose the genre simply because it's hot right now, you're doing it for the wrong reasons.
First of all, genres go in and out of fashion. A lot of dystopian novels have come out recently. However, if you start writing a dystopian story right this minute, by the time it gets published the whole dystopian craze will have most likely faded. Publishing takes a long time, usually two or three years. Don't rely on current fads when deciding which story to work on.
The other issue is purely coming from an artistic standpoint: if you don't love the story idea, your book isn't going to be the best it can be. I learned this with ENCRYPTED. I was never very passionate about the story concept, so it didn't turn out as well as I had hoped. When you write what you want, you're tapping into the passion that drives most artistic ventures, and this will naturally reflect in your writing/characters. Never settle for something less; in the end, you'll probably regret it. I think a perfect example of this is The Adoration of Jenna Fox by Mary Pearson. When she first wrote this book, people told her it wasn't "commercial" enough to be published and reach a wide audience. I personally adored the story - it's become one of my favorites, and I have to say, I am so glad Ms. Pearson didn't listen to what other people told her.
In conclusion, write what you want. Write what you love. Don't get caught up in trends, because when it comes down to it, trends eventually fade. Good writing will never go out of style.