Hi Dayglow,
I own the AS Challenger and I think it is a good choice. I have not owned the other two but I have heard Rega RP8. I considered the Avid and the Townsend Rock 7. But the affect of mass on rotation stability and bass response swayed me to the ASC. I am not sorry about my choice. The sound is expansive and neutral. It is also super quiet. I think you would have to go a lot higher on cost to get comparable quality and performance.