I was a Line 6 hater for years. Especially when I joined a band and the other guitarist was using a Line 6 head (it was the chrome one with the blue light, I forget the model) and it sounded quite bad. It was somewhat acceptable for lone basement playing, but live with a band, it was not good.
A few years later I was looking for a modeling combo amp that I could use for quick low volume practice at home and with the band, and in a pinch, use it for a gig. A local working guitar player (who is an UNBELIEVABLE guitarist, chops for days) used a Line 6 Flextone III combo for all his bar gigs. He was also in my band before me. I asked what he used on the bands recordings and he pointed to his Flextone! I was shocked so I monitored the local Craigslist looking for one on the cheap. A few months later I found one and have been happy with it. Happier than I EVER thought I would be with a Line 6.
A few months after I purchased the amp we opened for Stryper. Due to extraneous circumstances I was forced to use the Line 6 for the gig instead of my EVH/rack rig. It held it's own and got me through. Wound up being one of our best gigs! I found that it sounds much better live mic'd with a E609 vs an SM57. I don't like it as much direct.
Also, the guitarist from the show "Live from Daryl's House" uses a late model Line 6 combo and his tone is excellent!
So, It all depends on how you dial it in, which model you play, and how it's ran through the PA.