I've played one SG Special (early '90s) that was very special, although most have been hit and miss. At the higher cost levels, I'd rather have a nice E-II Viper if going the metal route, they consistently kick ass....
If you want the classic SG look then any Epi G-400 is a solid option. Any of the red or black ones. People let them go all the time. They are plentiful and consistent.
I also have an Iommi G-400 from 2003 that's 23 years old but I only recently got a few years ago. I've since swapped the pickups out and blacked out the guitar.