I still pronounce it "Ghidrah."
The "but still" people of the 70s pronounced it "GHEE-do-ra." (which is also how Nick Adams pronounced it, as well as the rest of UPA's dub of Monster Zero). I also pronounce it like this.
Toho's post 80s International dubs pronounce it "ghuh-DOHH-ruh," the absolute most RETARDED pronunciation ever. I know they're the same crew as the "but still" dubs, but they've gotten worse since the mid-to-late 80s. They were definitely better back then. They're pretty lazy now (partially because Toho rushes them; Back then, they had a lot more time).