What's better: funny or serious? That's a question you might hear from Beck Bennett, the suited-up star who interviews rambling children in AT&T's latest ad campaign. Bennett, 28, got the gig after showing the casting director a series of similar videos he'd posted on YouTube. (Look up Fresh Perspectives. You'll thank us later!) He also has a Web series called Theater of Life, which is sort of a crass version of MST3K set on Venice Beach, and he's one-quarter of Good Neighbor, a comedy troupe he created with three friends, which recently tested a pilot at Comedy Central. The success of the AT&T ads has been especially gratifying, he says. ''It's like going through a coin level in Mario Brothers.''