The verdict
For a small B2B or SaaS team that wants to be running in a day, I'd pick Help Scout. It stays simple, it has a free plan to start on, and the knowledge base comes from the same vendor. If you already know you need ticket fields, SLAs, several channels including phone, and a wide set of integrations, pick Freshdesk.
The trade-off is setup. Freshdesk takes a few weeks to configure properly, and a badly configured helpdesk is worse than a shared inbox. Help Scout is quicker, but advanced workflows and single sign-on sit on higher plans. Test the AI on your own tickets in either tool before you rely on it.