Stick to one genre?

IMHO the answer is YES!!! But, let me clarify.

I fully understand the desire to try new things. I also understand that for many new writers, finding that niche for you is often difficult. With that said, just jumping from one project to the next and one genre to the next is not going to help you.

If you ask most established writers, it took them a while to find their voice. The thing is, they all took the time to really work through the genre before moving to something new. You can not tell if that genre will work or won't work for you until you have had a chance to try it out.

But, the story sucks you say...

Sure, but that doesn't mean the genre is bad for you. There are numerous factors why the story didn't work. It could be the plot, the characters, the setting? It could be that you didn't think it through clearly. Shifting to a new project and genre is not necessarily the best thing, until you can figure out what didn't work.