The verdict
For a lean B2B founder, install Google Analytics first as your source of truth for traffic and conversions, then add Microsoft Clarity the same afternoon to see what the numbers can't show you. They cost nothing, they share data (Clarity integrates with GA4 and Google Tag Manager), and they answer different questions, so treating this as an either/or is a false choice.
If you are genuinely forced to pick one, the deciding question is what you're trying to fix. Chasing where traffic comes from and whether campaigns pay back? Google Analytics. Trying to understand why visitors bounce off a page that should be working? Microsoft Clarity. For most founders the GA4 numbers come first, because you cannot optimise a funnel you can't measure, and Clarity is the diagnostic you reach for once GA4 has flagged the page that's leaking.