I've been a fan of Daily Show since the beginning. I still have a soft spot for Craig Kilbourne. He never took himself too seriously and had some segments that were just completely WTF???. The show was great in the early years when no one knew who they were and they could do features where they totally ambush people Ali G/Borat style.
Daily Show is still very good. But I would say its peek was 1999-2003-ish. It's gotten way too partisan lately for me.
However, The Daily Show is starting to replace Saturday Night Live as THE American TV show for breaking comedic talent. Steve Carrell is a huge star now. Stephen Colbert is a household name. Ed Helms has a great role on The Office. Rob Cordrey got his own show for a bit. Lewis Black is A-list on the stand-up circuit.
Who's SNL given us lately? OK, Tina Fey but who else? Jimmy Fallon never quite broke big outside SNL. Amy Poehler, meh, still kinda a B-list character actor. Will Ferrell was the last BIG star but he left 6 years ago.