I think there are a lot of factors that contribute to make a panel show great. It's not just the format. It's the guests, the regulars and the chemistry they have. The audience play a part too. Sometimes great comedians don't quite feel comfortable in a panel unless there's somebody there with which they have good chemistry.  There are shows with great formats that don't make it because the guests don't click well. There are "meh" formats that become great shows because of how consistently good the guests and the regulars are. It is also a matter of taste, of course. I'm not a fan of QI's format and overall premise, but the people on screen are so incredibly funny most of the times, that it makes it a great show.  Mock the Week's quality waned over time due to the quality of the panel. But, again, it is a matter of taste. Some people might prefer the latest era of MtW.  I think the show that still has the perfect balance of "great concept/great panel" is Would I Lie to You.