As a startup, you're resources are extremely constrained. Your most constrained resource is time, esp when you have customers. The hard fact is that you really

As a startup, you're resources are extremely constrained. Your most constrained resource is time, esp when you have customers. The hard fact is that you really can only focus on one idea, so make the most of it and pick the one that you're most frustrated doesn't exist yet. Popular advice these days is to just do something you're really interested in, but it's resulting in a bunch of redundant nonsense in popular spaces like music and geolocation social networks. I would only do something based on interest if I had a really unique offering (Turntable.fm comes to mind). Otherwise, focus on something that just sucks and that's begging for a solution. You don't need to convince the market that they want/need what you have. They already know they do and have been waiting for it. If you can do something that you're uniquely positioned to do, even better. Best of luck!