I would start by looking at the product description and then the product design. Does it make sense? Does it feel like you can use it as a user? How does it work? What are the key features and benefits?
Then I'd look at the team behind the proposal. Do they have a lot of experience creating software products? Do they have any past successes that will help them succeed with this proposal?
Finally, I'd look at their marketing plan for this product. Is there an actual plan for how they're going to market it and how much money they expect to spend on marketing? Are there any partners involved who might be able to help market the product?
All in all, though, my best advice is just to look at all 10 proposals fairly closely and make your decision based on what feels right for you!
