I haven't taken any tours in Berlin, but I'm sure others have. What type of tour are you interested in? That will help responders provide suitable suggestions.
Berlin has a lot of historical sites. Many of them have museum-quality explanatory material posted, so I'm not sure a tour would add a huge amount of value in many cases. Because of heavy wartime damage, much of the architecture in Berlin is fairly modern; if you take a walking tour, you won't necessarily be seeing a lot of beautiful old buildings. And of course Berlin is huge and terribly spread out, so any tour's coverage is going to be limited.
I imagine there are walking tours focusing on the WWII period and others on the Communist period. Those could be very interesting, but it would be possible to spend 3 or 4 days in Berlin just at the key 20th-century historical sites.
Perhaps a trip to Potsdam would suit you. I haven't been there, but I understand it's very pretty as well as being of historical importance.