Did offering an annual discount actually improve your customer retention or just help cash flow?

We've been debating our pricing model for a while now. Monthly sub plans make our sales funnel flow smoothly but our churn resets every 30 days and we have to keep winning the same users back. On the flip side upfront yearly billing gives us great cash flow but the friction at checkout is much higher for new visitors who don't know us yet.

How did you balance your monthly versus annual options when starting out and did yearly plans actually make buyers stay longer?