South Mountain site does not carry a lot of interesting talkgroups. Below are examples of talkgroups currently active on the South Mountain site:
1401 Light Rail Ops 1
1405 Light Rail Maint 2
1406 Light Rail Security
1501 Solid Waste North
1513 Solid Waste East
1515 Solid Waste South
1517 SR 85 Landfill
2192 DPS Encrypted
4555 Maricopa Community College
Thompson Peak site carries similar talkgroups, but carries a couple more "interesting" talkgroups:
2811 A2 Phoenix PD 200
2808 B2 Phoenix PD 200
3402 A2 Scottsdale PD2 North
They can change what talkgroups are carried on what sites, so these may change in the future. When they took Simulcast C down for change to 700mhz, they were carrying a lot more of the "interesting" public safety talkgroups on the high sites. Today, most of the interesting talkgroups are only carried on the Simulcast sites. White Tanks does seem to be the exception, carrying a few public safety talkgroups.
Also, I believe the rarely used O "Ocean" Interop talkgroups are used on the high sites, so keep them programmed for when these talkgroups are active with an event or incident.