Don’t understand why anybody would consider the GT-8 over the GT-10. The new one is better. And its more hard-wearing than the plastic body of the line6. The vox doesn’t have as many options as the other two, but its got a valve in it so the tone should be really good.
So if your looking for a robust live pedal then its betweent the Boss and the Vox, but i don’t know much about the Vox so I say GT-10. if its between the GT-8 and the Line6 go for the Line6
I haven’t had personal experience with the GT8, but from the GT5 and GT6 pedals I used to have, I can’t recommend the Boss route very much. I was never able to get good distortion tone from those pedals at all. Granted, they may have improved in that department with the GT8 or GT10.