Best way to tour the Sagrada Familia

That's entirely down to your preferences...

To me, for example, I would rather tour on my own at my own pace, so for me, it is the audio guide -the one provided by Sagrada Família when purchasing the ticket "Sagrada Família with tower"

I really liked the tour offered by the official website of the church, which included an audio guide so that I could go back and listen to it at will as I wandered around afterwards. I did the tour first at 09:00 or so and then stayed for another few hours, visiting the museum, wandering around, taking photos. Best of both worlds.

Before we went to Barcelona, I did a lot of reading and watching videos about the Basilica, so we just bought entry tickets and we were our own tour guide. We went at our own pace. We were able to just sit or wander around and take it all in for a couple of hours.
The inside is one of the best things I've ever seen. So colorful, so original, so well done, I can see why the Catholic church has started the beatification process for Gaudi. Every now and then the human race justifies its existence when someone creates a monumental work of art.

But anyway, why not study up a little so you can be your own tour guide and have ultimate freedom to enjoy the place at your own pace?