A second assignment approach is by category. For example, a salesperson has the health and beauty category, so any clients within this vertical gets assigned to him. This makes things clean and simple, and in theory, induces expertise within the category covered.
A third approach is straight-out account assignments. Here is your list, it dabbles across verticals but aligns by territory -- now go get 'em. Of course this is optimal, but it's not working in today's climate (more on that in a second).
Which leads to ad agency assignments -- meaning a salesperson handles all of the business at Beyond Interactive for example, regardless of the client. This approach, when coupled with regional guidelines, is the most effective. Here's why.
We are in the relationship business; so you should throw out any approaches that emphasize something you can't take out to lunch -- and you can't dine with a "category." That set-up of course leads to client contacts, but it also induces a sense of entitlement. A rep is fast to claim, "that's my account" when an RFP comes through to the main email address and not his own because the client is within "my category." Why should a salesperson be entitled to earn business he or she didn't even know was in play?
The same thing can occur with the agency assignment approach (an RFP comes in from a group the rep was not calling on) -- but in this case, the word will get out to the new group if the salesperson has done a good job servicing that agency.
Agency assignments create the most fertile ground for relationships to cross-pollinate. Calling on Wieden & Kennedy for Nike helped me break Microsoft in the same magazine. Conversely, when buying ad pages in Newsweek for U.S. Postal, I did not give the same magazine much consideration when a different rep called on me when I was spending for Kodak. Had my rep on U.S. Postal been assigned to Kodak, Newsweek would have stood a better chance, because the relationship was already in place. It's human nature.
Back then, ad agency assignments were not the norm because back then clients always saw reps and relationships were truly developed. Today, client relationships are claimed on the knowledge of the client's name and where their offices are located. And for the exceptions when a client relationship is cemented, you can assign that salesperson the agency his client is using. If this is not feasible because the account moves to an agency being properly covered by another rep, then you can exercise a split.
Client relationships are vitally important and should be developed whenever possible, but they can coexist with a primary sales assignment approach that emphasizes blanket coverage of ad agencies. The opposite way, making client account assignments the dictating force, causes faulty claims and a sense of entitlement, and sends multiple sales voices into the same agency.
If you commit to an agency-centric approach, your sales call coverage can and should expand to creatives. No one ever calls on them, which is why you should. Doing so would likely help lead to creating a big idea worthy of the media buyer's attention.
Whichever approach you choose to emphasize to steer your sales organization, commit to it as your primary guiding force, and it will work. The problem occurs when you try to make them all work at the same time.