Take my site for instance, it's about cheap VPS deals. I'm a big fan of VPS's and definitely cheap ones, so this niche made sense to me, and within a month my site has skyrocketed on search engines and all over because my passion and hard work bleeds through on the site. Granted, I'm not #1 in my niche yet, because i'm battling a behemoth that's held their ground for 4 years, but in a very short time i've conquered quite a bit of ground and I expect to conquer a lot more in months to come. Part of this was for tactical reasons(I launched when they were down hehe, always have to take advantage of opportunities!) but most of is just hard work, and that's because I want my site to be the authority for its space, I want it to be #1, so everyday I work on it, making it better.
So find what you enjoy and go after it! It doesn't matter if it's health, wealth, or sporting niches, if you put that extra effort in i'm telling you people will take note. Google hasn't climbed the ranks and completed dominated their space all this time because they look pretty...they did it because of an amazing product, that's had a lot of passion put into it. In fact some of you may not know this but for a long time Google did 0 marketing for their site, they just kept getting bigger and bigger because of word of mouth!