The verdict
If you are a freelancer or a small agency that wants tidy, trackable proposals and invoices to follow, I'd pick Prospero. It has one published plan, so there is little to decide and little to overpay for.
If you run deals from a CRM and want the proposal to feed the follow-up, I'd pick Better Proposals. It has the deeper integrations, the nudge-style follow-up and the payment and onboarding steps after signing. The catch is that CRM integrations, a custom domain and API or Zapier access start on the Premium plan. Price that plan, not the entry one. For most small B2B teams on this site, Better Proposals is the safer choice.