One thing that bites a lot of teams with HubSpot routing is the order of checks. Put your exceptions first: existing customers and named accounts go to their account owner before any territory or round-robin rule runs, otherwise a new contact from a key account lands with a random SDR. Then do territory, then rotation.

Two practical tips. Add a fallback owner (or a shared queue) for anything that matches no rule, and set a daily view of contacts with no owner so gaps get caught fast. Also normalise country and company size values with dropdowns or a cleanup workflow, because free-text "USA" vs "United States" quietly breaks branch conditions.

Finally, test with five or six dummy contacts covering each branch before turning it on, and add a rule that skips reps marked out of office so leads don't sit for days.