Salesforce is built for massive enterprise teams with highly complex processes and the budget to hire consultants who can map everything correctly. If that's you, Salesforce handles complexity that Streak can't touch.
Streak, on the other hand, tries to bolt CRM features onto Gmail, but quickly turns messy and bogs down with any real volume. It ends up feeling like a clunky spreadsheet grafted onto your inbox, and doesn't handle scale or complexity well at all.
If you actually need a CRM for serious business processes or plan to grow, both reviews make clear that Streak falls apart fast. Unless you're absolutely committed to staying inside Gmail and working off a glorified spreadsheet, there's no reason to pick Streak over Salesforce for handling CRM needs.
But if you're not a huge enterprise with deep pockets and complicated workflows, neither is a great fit. Salesforce is only worth it if you're running a massive, complex operation and have the resources to do it right. For anyone else, skip both and look at more user-friendly CRMs.