• Fit for purpose
  • is it good for solving the problem you're solving
  • does it scale to the scale you need
  • does it have integrations that you need
• Stable tech with solid community
  • so if you hit a problem there's a high chance of finding a solution quickly
  • you're a solo operator, you don't really want to be the one spending a week finding the solution!
• Skills available on the market for when you grow
  • consider both permanent and contractor availability - if you need someone for a couple of weeks to help ship something fast, could you get them?
• Cost (including licensing, hosting, etc)

Hope that helps.

If you are a developer and have been into development of any kind, then you should first consider the tech stack that you are currently working on. If you are confident in it, then you should use that. Don't get into all the shiny new tech that you don't have any experience into.

Remember, you would want to build a MVP as soon as you can so that you can refine your product based on end user feedback and make it better in less time.

You can always figure out ways to scale your product no matter what tech stack you are using by having skilled employees by your side. For example, Quora and Uber mostly uses Python as it's main language. Now matter how people say that Python is not good for highly scalability but if you have a skilled and dedicated team on your side, you can always build tools to achieve what you product demands.