One Aruba best practice for this design is to ensure that optimization and suppression of unnecessary multicast is enabled on the MCs. This is because multicast traffic can consume a lot of bandwidth and degrade the wireless performance, especially in a large building with many devices. By enabling optimization and suppression of unnecessary multicast, the MCs can reduce the amount of multicast traffic that is sent to the APs and the wireless clients, and improve the network efficiency and user experience.

Option A is incorrect because extending VLAN 10 to the edge and deploying Aruba APs on it is not a best practice for this design. This is because it creates a large broadcast domain that can increase the network congestion and complexity. It also exposes the VLAN 10 to potential security risks from the edge devices. Option B is incorrect because ensuring that each user role on the MCs is associated with a different VLAN ID is not a best practice for this design. This is because it creates a large number of VLANs that can increase the network overhead and management difficulty. It also limits the flexibility and scalability of the network design. Option C is incorrect because ensuring that the RADIUS server assigns users to different VLANs dynamically is not a best practice for this design. This is because it adds an extra layer of complexity and dependency to the network design. It also requires the RADIUS server to be configured and synchronized with the MCs and the VLANs, which can introduce potential errors and delays. References: Aruba Validated Design: Campus Wireless LAN), ArubaOS 8.7 User Guide)