AAA debugs are by far the easiest and most common mechanism for troubleshooting AAA issues. Although you can use show commands to check the various stages a negotiation is in, debugs are by far the best sources of information for failing AAA setups.
AAA show commands are often used in conjunction with debug commands and play a supporting role to the debug commands. However, they can often be used to gather summary information about the status of the AAA features and the TACACS+ and RADIUS feature sets. This can come in handy when you troubleshoot AAA-related issues. Some of the commonly used show commands for TACACS+ and RADIUS are
show radius statistics
show caller user userid detail