We did all the Hollywood studio tours last summer. Although we enjoyed the tour we found it very scripted, plus there were so many tours going on at the same time. They are very diligent about when you can take pictures, half an hour of the tour is spent in a museum looking at costumes (you are not allowed to take a camera in there either.) The best part of the tour for me was going to Central Perk as I am a huge Friends fan.
Our favourite tour we took was the Paramount one. There were far fewer people on this tour, there was only 6 of us on the tour and we were the only tour that morning. It was a lot less scripted and the guide let us take pictures where ever we wanted to. We were allowed off the carts and to wonder round a lot more. We got to go inside a studio where they were filming an episode of Everybody hates Chris, we stood with the director as they did a few takes and we watched what was going on on the monitors. We also went into the studio next door where they had more of the set and we were allowed to take pictures where ever we wanted to. We also went into the post production room of Entertainment Tonight where the presenter was recording some links for that evenings show. We chatted to him for a while, he explained how all the consoles worked and he posed for pictures with us. We also got ot walk around lots of the outdoor sets, through the doors into the flat buildings etc.