Attribution model selection depends on three factors: sales cycle length, channel diversity, and data volume. If you're running paid search only with a 1–3 day conversion window, last-click attribution works fine because most touchpoints cluster together anyway. If you're running SEO, paid social, email, and retargeting with a 30–90 day cycle, you need position-based or data-driven attribution to avoid systematically undervaluing top-of-funnel channels. Last-click gives 100% credit to the final interaction. It's simple and matches how most Canadian small businesses think about conversions, but it ignores the SEO article or Facebook ad that started the journey. First-click does the opposite, crediting only awareness channels. Linear splits credit evenly across all touchpoints, which sounds fair but treats a brand search the same as an initial blog visit. Position-based (U-shaped) assigns 40% to first touch, 40% to last, and 20% distributed in between. Time-decay gives more weight to recent interactions, useful when you know proximity matters. Data-driven attribution uses machine learning to assign credit based on actual conversion patterns in your account. Google Ads and GA4 both offer it, but you need meaningful volume: at least 3,000 ad interactions and 300 conversions per model within 30 days for Google to train reliably. Most Ottawa businesses don't hit that threshold. At Ottawa SEO, we typically start clients on position-based attribution because it balances awareness and conversion credit without requiring massive data volumes. We compare it against last-click in parallel reporting for 60–90 days. If SEO and paid social show significantly higher assisted conversion rates under position-based, we know last-click was systematically underfunding them. For SaaS clients with 45+ day cycles, we lean toward time-decay because demo requests cluster in the final two weeks after multiple content touches. The wrong choice here doesn't just skew reports. It drives bad budget decisions. If you're optimizing to last-click data while running a multi-touch strategy, you'll keep cutting top-of-funnel spend that actually drives pipeline. Run dual attribution views in GA4 for at least one full sales cycle before committing to a model for budget allocation.