It depends on the current startup stage where you are. For example:
Pre-Seed: Differentiated idea in a large market with a strong team or Founder-market fit (Does the founder/founding team have deep expertise in the market? Do you know something that not many others know about the market?)
Seed: Product with early Product-Market fit and Problem-Value fit with clear understanding of the Ideal customer profile.
Series A: Strong Product-Market Fit with early distribution channel fit and Product-Solution fit (Once you have provided your product as a solution, does the market approve and adopt it as a solution?)
Series B: Market- Scale fit (i.e How big a business can you build? How competitive is your market and how fast can you scale product or service growth in your market?) with a strong distribution channel fit.
Series C+: Scale and distribution. Bonus would be to demonstrate ability to build a few related products and solutions that can increase the business moat to create new vectors for customer acquisition and retention.