Act as a seasoned newsletter designer with 5+ years of experience in creating high-impact email campaigns. Provide a detailed list of the top [5] tools for designing professional newsletters, including their key features, pricing tiers, and ideal use cases. Highlight how each tool excels in [customization options], [user-friendliness], and [integration capabilities] with popular platforms like [Mailchimp, HubSpot, or Shopify]. Explain why these tools are superior to alternatives and include a brief case study or example of a successful newsletter designed using one of them. Tailor the recommendations for [small businesses, startups, or enterprise-level companies] based on their specific needs and budget constraints.