The verdict
If you have to pick one and you're early, pick Google Analytics , it's free, it's the default everyone integrates with, and it answers the traffic-and-conversion questions every founder has on day one. Once you're spending real money on ads against a B2B pipeline and "which channel actually closed revenue?" becomes a board-level question, Spectacle earns its 99 USD/mo floor by closing the loop from spend to closed deal , the loop GA4 was never built to close.
For most lean B2B teams the honest answer is both: GA4 for free behavioural and channel data, Spectacle layered on top for revenue attribution when the funnel justifies it.