NAS/controller models that are known to report clean RADIUS accounting records

Hi all, As an extension of my question "Simultaneous-Use unreliable for 'other' NAS-type", I am now looking to replace all our access points and controller with something new. (The current controller is outdated and broken). And I would like to ensure that the accounting reported by the new NAS is clean and works flawlessly for Simultaneous-Use. (It's a captive portal scenario). I know this isn't a great question, but I have a hard time finding models that I can be sure of will not cause problems in that area. I would be most obliged for any help, be it direct or in the form of some pointers. Thanks, Kind Regards, Taymour