This is case specific. Here are a few things I would consider from my experience with MVP's:

- focus on usage, not number of people using
- # of Downloads
- # of Downloads that use product (tie this to relevant metric e.g. if you're mint this could be linking 2 financial accounts)
- Whether people will pay you to use your product
- if freemium model, what % are paying and how can I convert more of them
- are you creating an investable story - e.g. there is a big market, I am solving __ problem, X # of people have this problem, y/x are using my app with no marketing, X LTV is Z, and no I need money to find more X's etc
- you personally still like what you're doing

Hope this was helpful. I am happy to chat more about this in more detail