Act as a seasoned digital marketing consultant with 10+ years of experience helping startups scale their email campaigns. Provide a detailed comparison of the top 5 email marketing tools tailored for [STARTUP SIZE: small/medium/large] startups with a focus on [KEY FEATURES: automation, affordability, scalability]. Include pros and cons, pricing tiers, and integration options with [POPULAR PLATFORMS: Shopify, WordPress, CRM systems]. Highlight which tool is best for [SPECIFIC USE CASE: lead nurturing, transactional emails, or customer retention] and justify your recommendations with real-world examples or case studies. Ensure the analysis is data-driven and actionable for founders with [BUDGET CONSTRAINT: limited/moderate/high] resources.