Rob,
Well as a single traveller I've done both solo and with a group (JY) and enjoy both, I can tell you I doubt you'll be disapointed been with a group is great fun.
Not done Sorrento but have done Andalucia and thought the excurrsions excellent (my fav was gibralter but others thought Alambrha palace, but all are interesting), its a good holiday.
Mick