I used to always just go for Metal Casting as it was the most expensive of the "sure bets." But nowadays I often go for Code of Laws to snag a religion (not so much for courthouses as I am building those somewhat later lately) and twice lately have snagged a real prize (1x Feud and 1x CS). I think I oracled HR once, but generally I just don't have the heart for oracling "cheap" stuff like HR/Alph/HBR/IW (shudder!) even though I know in my head that it can be useful.