Removal or Reformat?

Last month, I discovered the rootkit.zeroaccess virus had infected my PC, along with a strain of BackDoor.Generic virus. In my attempts to remove these viruses using several methods including Kaspersky HTKILLER and Malwarebytes Free, the OS was damaged removing my internet access. I attempted repair of XP, but could not with the older version I had so installed a different XP without formatting. I installed AVG and scanned, finding that the computer is now infected with the Crypt.ANVH and BackDoor.Generic14.GVG viruses. One problem seems to be that my external hard drive is also infected.

After reading several instructions on removal of these viruses, I wonder, would it be easier to reformat and reinstall XP on a clean hard drive rather than bother with the removal process? All data is backed up. I am very frustrated! I sincerely appreciate your advice on this matter.

Also, if I do start over from scratch with a fresh format and XP install, what antivirus would you recommend?