It really depends on the needs of your organization.
Attended concurant is useful if you have users who will work in shifts, as the license is only consumed when users log in to the machine. For instance, if you have a day shift of 10 users and a night shift of 10 users, you could use 10 attended concurant licenses to cover both shifts.
Attended named user licenses are intended for settings where the business users will require access at any given point in time during the day and cannot share their license. In the above example of a day shift and night shifts with 10 users each, you would need 20 named user licenses to cover both shifts.
20 licenses obviously will cost more than 10 licenses, but business requirements might necessessitate that named user licenses be aquired over concurrent.
There is no set “standard” as every organization is unique. You have to look at the needs of your organization to know what is right for you.