Mystery, thriller, and romance sell the best.
They're also the most competitive.
The best genre for you is the one with the best overlap of what you love and what the market loves and where the market is hungry, or at least not over-saturated.
Sometimes, it is hard to tell how saturated a niche is. A niche with a lot of books might still have room in the market. A niche with few books might be oversaturated. Talk to authors, follow their careers, stay up to date on what sells and what people are doing.
The saturation of the market changes with time, so IMO, the best thing to do is pick a niche but keep it flexible. Write PNR, but switch from, say shifters to werewolves when shifters get saturated. Or start writing RH shifters. Whatever interests you and has room for success. Those are made up examples because I don't follow PNR.
You can't pick a niche and stay there forever. If you succeed, people will notice, and they will come and saturate that niche. Often, people don't really get why you succeeded and copy the wrong thing and fail. But, eventually, if you have found a unique (enough) niche, people will come and fill it.
There is no set it and forget it.