Code of Laws with the Oracle. Depending on situation I'll occasionally take Metal Casting, but I go for Theology with my second Great Prophet, for the Apostolic Palace. (I am a religion whore; at the level I play on it is possible to get most if not all religions - because someone usually beats me to Buddhism and Wang Kon likes to bulb Philosophy, but still - the revenue from shrines helps enormously in balancing my budgets!) If I'm Sumeria and have early Ziggurats instead of Courthouses, and when I'm the Zulus and have access to the Ikhanda earlier still, then I might well go for Metal Casting because I won't need Courthouses/Rathauses so much.
Almost missed it this evening by delaying Writing and building the Oracle earlier than usual because Paris was a good starting point and Orleans an even better production facility, so I had SH and GW early too. It was a race to see which would be completed first, Writing or the Oracle. Luckily Writing won by about one turn, so perhaps I would have been better off taking Metal Casting at that point, but oh well...there you go.
With Liberalism, it varies (depending on when I go for it - and I usually get it because I accelerate away quite nicely in technology after the early stages of the game); sometimes Replaceable Parts, sometimes Nationalism, sometimes Military Tradition. When it comes along I'm usually embroiled in perpetual warfare, so unless I need the revenue from something like Economics or Printing Press, I will go for those kind of military technologies.