I never understood the fascination with Willow either. She was given a lot of funny lines, but the character and the actor were just too coy for my tastes. But Hannigan's the only one of the Buffy cast to make it Big Time. Spike was my favorite character, but James Marsters's career pretty much tanked once the series ended. He's made a comeback of sorts, in a number of guest shots on TV series and the lead in an unreleased fantasy movie called Dragon Warrior. Sarah Michelle Geller's last short-lived series proved she still hasn't learned how to act. Emma Caulfield was wonderful as Anya, but she too went the guest-star route like everybody else. She has roles in two movies now in post-production; maybe one of them will be her breakthrough. I also liked Giles, except when he was singing. For Anthony Head, there has been life after Buffy; but even though he's had little idle time, he's not broken through to the stellar reaches yet. Example: he auditioned to play Doctor Who but didn't get the role.
But none of these people have earned anything like the $7 million Alyson Hannigan collected last year. Like her or not, she is the Buffy alum who has emerged as The Star.