The official guided tour for Park Guell costs €7 per person over and above the entry fee to monumental zone.
Tourists will benefit immensely from the tour as the guides explain the significance and artistic context of the various features at the Monumental Area of Park Güell. The tour covers key attractions of Monumental Zone : Austria gardens , main entrance, Monumental Staircase, Hypostyle Room, laundrywoman portico and Nature Square. The tour is for one hour. Once the tour is finished, you can remain inside the Monumental Area.
There are 4 sessions in English. Check the timings and book in advance.
To reach Park Guell, bus route no 24 is the best option. You can alight at Carretera Carmel-Park Güell stop, near the top of the hill, which is one of the main entrances to the Park. It is also the meeting point for the guided tour of Parc Guell.
Skip the guided tour
I see no benefit in taking the guided tour of Park Guell. There is a lot of information available in the park itself, apart from the material online.
Park Guell is not like Sagrada Familia or Casa Batllo where you need to explain the layers and the thinking behind the architecture. It is just a park with fantastic works by Gaudi.
But you must definitely buy the ticket to the monumental zone, spend time here before you go to the free hilly areas.
Skip the Gaudi house museum; it is nice to see from the outside, the inside is nothing great.