Joking aside, do you already know what time (and day) you'll be back in Rome from Terracina?
Because you can have different scenarios due to ZTL time, working/offices time and so on...
For example, you will arrive from Terracina driving on Via Pontina (taking A1 highway will make you waste an extra hour, so forget it!) that is in the South so there's no benefit to drive to Tiburtina/A24 (highway) that's in the eastern part of the city.
That said, your best choice should be #10 for these reasons:
- inner/clockwise GRA highway in that tract (exit 26 to 1) is usually less traffic victim (expect "early" morning)
- from #10 to Pantheon area will take only scarce 15 minutes with normal traffic (half an hour if really busy)
- though Terracina-#5 would make you spare about 10 minutes, the total voyage Terracina-#10-Pantheon will last surely less than Terracina-#5-Pantheon cause the Via Appia is usually quiet busy and you should "cut" the whole citiycentre while Vatican-Pantheon is better and faster connected