Stewart greatly admires Beavis and Butt-head and believes they are his best friends - they are not. Aside from bullying him, exploiting him, and dissing him for sucking, in "Drones" Beavis actually forgot Stewart was alive and they saw him yesterday.
Daria had no interaction with him in the show but several in the comic series. In those comics, she didn't think much of Stewart at all and lumped him in with Beavis and Butt-head as people she didn't want to see on Halloween. Once, when Stewart was about to stop the lads being left behind in Amish country, Daria threatened him into silence.
In "It's A Miserable Life", we see if Butt-Head had never been born, Beavis and Stewart would be best friends and do charity work. Stewart in this alternate universe is more assertive, as shown by him wearing a Poison T-shirt.