Should I ask for Android app recommendation on main site or on Software Recommendations?
No, app recommendations are off-topic for us, just because they don't work very well with the SE format, which favours questions with an objectively correct answer. That said, if you have a specific problem to solve, and the answer might be one of:
- App X can solve your problem
- You need to install a custom ROM to do that
- There isn't an app, but if you do A in app X, and then B in app Y, then it'll solve your problem
and you'd be happy with any of those answers, then your question isn't an app recommendation: it's a problem-solving question. In that case, it's fine (unless it's off-topic for a different reason, such as you're trying to use an iPhone, not Android).
Good software recommendation requests have two components:
- A purpose — a task to accomplish, a user story
- Some objective requirements — a minimum set of features
If your question has those, and you're definitely looking for an app, then your question is probably a better fit for that site.
If you don't have a purpose or objective requirements - for example, your question is "Which music player should I use?" - then your question probably isn't a good fit for any SE site, because of the aforementioned limitations of the format. In that case, you should probably ask on a discussion forum or on Reddit, where questions can be completely subjective and have many answers.