Like you said, it will vary from product to product. Will also vary based on the long-term goal for that product.

Are you going for the lowest common denominator and the mass audience? Or are you going for a niche market?

For products that want to reach the lowest common denominator and the mass market, the product must have as less friction as possible. This most likely means free and clean. To be able to do this, you will need to raise money up front and keep raising money while growing your bottom line user base and activity. Then once you reach your critical mass, apply x,y,z revenue model.

For the niche market, you can usually find people who are willing to pay upfront for your product. However, your goal is not about explosive growth so applying x,y,z revenue model is okay.

Hope that helps you out!