Let me add my personal ratings, since I have done them all.
By far, my number 1 is the Universal VIP Tour, which is much more than just a small personal group touring sound studios and backlot areas, but also meals and the Theme Park experience.
http://www.universalstudioshollywood.com/tickets/vip-experience/
Age limit is 5+ and photos/videos are allowed for almost all experiences.
Number 2 doesn't get mentioned a lot, but is interesting, and that is the Sony Pictures Studios in Culver City.
http://www.sonypicturesstudiostours.com/
A walking tour, Age limit is 12+, photos/videos mostly allowed. Weekdays only.
Number 3 would be the Paramount VIP Tour.
http://www.paramountstudiotour.com/vip-tour.html
Age limit is 10+, weekdays only, I prefer the Morning tour with lunch.
And at the bottom is the Warner Bros. Tour.
The Deluxe Tour is the best, but about the same price as the Universal VIP, and is a lot shorter and only one meal.
https://www.wbstudiotour.com/deluxe-tour
Age limit is 8+, photos/videos are severely restricted. (Your camera is usually locked up in a box on the tram).