Whichever department answers the same question most often.
That is usually support. Occasionally inbound sales. Almost never the department that asked for it, which tends to be whichever one has recently read something about AI.
The test
Go to each team and ask what they answer most in a week.
The department that can immediately name three questions with identical answers, sitting in a system, is your starting point. The one that says "it varies, every case is different" is not, however keen they are.
You are looking for volume and repetition, not importance. Important and varied is exactly what humans should keep.
Why support usually wins
Highest volume of repetition in most businesses. Order status, account questions, billing explanations, first-line troubleshooting. Enormous quantity, small number of shapes, answers already in your CRM or billing system.
It also has the clearest measurement. Contacts handled, resolution rate, satisfaction, recontact. You will know within weeks whether it worked, which matters more than it sounds because the first deployment is buying you evidence for the second.
When to start with sales instead
Two conditions.
You have a genuine out-of-hours or speed gap on inbound, where enquiries arrive and sit. Leads contacted within five minutes qualify far better than those contacted after thirty, and 35 to 50% of sales go to whoever answers first, so the cost of the gap is quantifiable.
Or your support contact is genuinely low-volume and varied, in which case the support case is weak anyway.
Sales tends to show a faster commercial number. Support tends to show a more defensible one. Both are reasonable places to begin.
The mistake to avoid
Starting everywhere.
Every channel, every department, every query type, on the theory that a wider launch demonstrates commitment. It does not. It produces something mediocre in six places, with nothing tuned well enough to prove the concept, and no way to tell which variable caused which result.
Pick one lane. Two specific query types, one or two channels. Get it genuinely good. Then add.
The second agent takes one to three weeks against four to eight for the first, because the integration layer, the knowledge layer and the escalation logic already exist. Most of the first build is foundation you only pay for once, which is why the rollout accelerates rather than repeating.
The other thing to check before choosing
Which department's systems can you actually get into.
A perfect use case behind a system nobody can grant access to is worse than a decent use case behind an accessible one. In our builds the go-live date has been set by system access nearly every time, not by the AI or the conversation design.
So the real question is a pair. Where is the repetitive volume, and where can we read the data. Where those overlap is where you start, and it is occasionally not the department with the loudest case.
