To Tell The Truth: Flip-flopped between this and What's My Line?. WML? nearly won out due to it being the pioneer of the G-T panel games, but I give the nod to TTTT for being the better show. There will always be interesting people who have interesting stories from all walks of life, and TTTT has proved that across seven decades at this point.
Jeopardy!: Still the granddaddy of quiz shows, having stood up to and outlasted stiff competition (looking at you, Millionaire). It's the pinnacle of TV quizzing competitions in North America and goes on my Mt. Rushmore because of that.
The (New) Price is Right: It's been going for 50 years and counting, so they must be doing something right. Price has ascended to icon status in the same way as J!, but for entirely different reasons. It's what we all watched when we were home sick from school. The fuzzy nostalgia factor has been leaned into more and more in recent years and the show is as popular now as it ever was. It's your "warm blanket" of game shows.
The $100,000 Pyramid (Clark): I'm being more specific here than with the other shows. Pyramid is, in my opinion, the best game show developed specifically for television. Easy to play, difficult to master, and Dick Clark knew how to command the proceedings. I defy you to find me a more dramatic, tension-filled moment than when a contestant is going for the $100,000, Dick calls for silence from the audience, and the studio goes so quiet that you can hear the air conditioning running. Then, when a contestant finally does win the big money, all that tension is released and it's bedlam. Lights up! Bells! Music! Audience bleachers empty! Television doesn't get more compelling than that.